Do you know your beltway from your bellwether? And what are blue dogs and red states? Use our guide below to help you navigate the election news.

Air war: The battle between candidates to get as much advertising on television and radio as possible. In recent years, online adverts, which are cheaper and can be more carefully targeted, have grown increasingly important.

Balancing the ticket: When the presidential candidate chooses a vice-presidential candidate whose qualities balance out the nominee's perceived weaknesses.

So for example, in 2008, Barack Obama, seen as young and relatively inexperienced, selected veteran Senator Joe Biden as his running mate.

Ballot initiative: A procedure allowed in a number of states under which citizens are able to propose a change in the law.

If the initiative's backers can gather enough signatures, the proposed change is put to the voters in a referendum. If it is approved by the voters it then becomes law.

Ballot initiatives are sometimes referred to as ballot measures or propositions.

Battleground state: A large state with an electorate split relatively evenly between Democrats and Republicans, so named because candidates spend a disproportionate amount of time and money campaigning there.

Traditional battleground states include Florida, Ohio and Pennsylvania, which have 29, 18 and 20 electoral votes respectively.

Bellwether state: A state that historically tends to vote for the winning candidate, perhaps because it is, demographically, a microcosm of the country as a whole.

A good example is Ohio, which has not backed a losing presidential candidate since 1960. In fact, no Republican has ever won the White House without the state.

The term derives from the name for a sheep which shepherds would fit with a bell. By listening out for this sheep, the bellwether, shepherds were able to locate the position of the entire flock.

Beltway: An American term for the orbital highway or ring-road that often surrounds major cities. In political reporting, the term refers to business undertaken inside the Interstate 495 highway surrounding Washington DC.

A beltway issue is a political issue or debate considered to be of importance only to the political and media class and of little interest to the general public. Those considered to have a beltway mentality are seen as being out of touch with the ordinary voters.

Benghazi: Islamic militants attacked a US diplomatic compound in 2012 in the Libyan city of Benghazi and killed four Americans, including ambassador Chris Stevens, while Mrs Clinton was secretary of state. The incident has become a hot political issue with Republicans blaming Mrs Clinton for the loss of life.

Bernie Bros: A pejorative term for (usually male) supporters of Vermont Senator Bernie Sanders who attacked Hillary Clinton and her supporters during the primary race. The abuse was often on social media and commonly misogynistic.

Bill of rights: The collective term for the first 10 amendments to the US constitution establishing the fundamental rights of individual citizens.

The amendments act as a mutually reinforcing set of rights and limit the powers of federal and state governments. Acts of Congress or laws ruled to be in conflict with these rights are deemed unconstitutional and may be declared void by the US Supreme Court.

The framers of the US constitution added the Bill of Rights in part because few individual rights were specified in the main body of the constitution.

Blue state: A state where people tend to vote for the Democratic Party.

Bundler: A person who gathers ("bundles") campaign contributions to a candidate from his or her network of friends and business associates.

Bundlers, who are often wealthy and well-connected, play a crucial role in contemporary campaign finance.

Individuals are barred by federal law from donating more than $2,500 (£1,603) per election to a candidate. But they can increase their influence by providing to the candidate cheques they have solicited from their associates and acquaintances.

The elite bundlers for President George W Bush's 2000 and 2004 campaigns were dubbed Rangers and Pioneers, a mark of their status.

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Capitol: The seat of Congress in Washington DC.

Constructed largely of white marble, it is home to both the Senate and House of Representatives.

The steps of the Capitol building are traditionally the stage for the inauguration of presidents on the 20 January following an election year.

Caucus: A meeting of party members and activists at which they choose which candidate to back for the party nomination.

In procedures that vary by state and party, participants in presidential caucuses meet in their local communities to choose which candidates they want to support.

The caucuses allocate delegates based on the level of that support. The results are then tallied state-wide, and the candidate with the most delegates is said to win the state.

Critics of the caucus system argue that its laborious nature tends to mean it is dominated by political activists whose preferences may not reflect those of the broader electorate.

Just under a dozen states use the system - the number is different according to party.

The most important party caucuses in recent years have been in Iowa.

In 2008, Mr Obama's victory in the Iowa caucuses - he won the most delegates - cemented his status as a serious contender for the Democratic nomination. It helped show Democrats elsewhere in the country that he could secure backing from white rural voters.

Citizens United: A 2010 Supreme Court ruling that overturned restrictions on corporate spending in political campaigns.

In the 5-4 decision, the court equated corporations' right to spend money to influence an election with the right to free speech held by individuals under the First Amendment to the US constitution.

It overturned a ban on corporate and union spending on electioneering communications - that is, so-called issue ads broadcast within 60 days of a general election (or 30 days for primary elections) which explicitly mention the name of a candidate.

It means unions and corporations will be able to directly advertise, right up until election day, as long as they haven't co-ordinated their advertisements with a candidate's campaign.

The Clinton Foundation: An international charitable organisation founded in 1997, originally to establish the Bill Clinton presidential library.

It has 11 major programmes focusing on agriculture in Africa, combating childhood obesity, economic development in South America, earthquake relief in Haiti, reducing the cost of Aids drugs and mitigating climate change.

It has become a focus for Republican critics who say that donors to the charity were rewarded with favours from Mrs Clinton while she was secretary of state. But there is no evidence of donors benefiting from the state department.

Commander in chief: The constitutional role granted to the president as head of the United States' armed forces.

Congress: The legislative branch of the US government as prescribed in Article I of the US constitution.

It is made up of two houses - the 435-member House of Representatives and 100-member Senate - each of which officially has equal power, if not prestige.

A congressional period lasts two years (or sessions) and begins at noon on 3 January of odd-numbered years.

As well as drafting and implementing laws, Congress can also:

- Investigate matters of public concern

- Oversee federal agencies and their programmes

- Declare war

- Approve and ratify treaties

- Regulate commerce

- Increase and decrease taxes

- Print and appropriate money

- Confirm/approve judicial and federal appointments and nominations

- Impeach federal officials including the president and vice-president

- Override presidential vetoes based on a two-thirds majority in each chamber.

Congressman/woman: A member of the House of Representatives, typically. The term can refer to a member of the Senate.

Constitution of the United States: The fundamental and founding law of the US federal system of government.

The US constitution and its 27 amendments establish the principal organs of government, their roles, and the basic rights of citizens.

It is upheld as the supreme law of the land, meaning all federal and state laws, executive actions and judicial decisions must be consistent with it.

The US constitution was ratified in 1788, and was most recently amended in 1992. It is the oldest written national constitution in effect.

Delegates: The party members whose votes at the national convention officially determine the two parties' presidential candidates.

Most of the delegates at the convention are obligated to vote for the candidate chosen in primary elections or caucuses in their home state. They are referred to as pledged or elected delegates. Some delegates, however, are unpledged and are able to vote for any candidate at the convention.

In the Democratic Party, these unpledged delegates are called super-delegates. They include senior members of the party hierarchy and rank-and-file members elected to the Democratic National Committee, the party's governing body.

Donkey, Democratic: The donkey has become the established - although unofficial - political symbol for the Democratic Party. Democratic Party historians say the symbol was first used during Andrew Jackson's presidential campaign in 1828.

Labelled a jackass by his opponents, he adopted the donkey for his campaign posters and it stuck with him.

New York cartoonist Thomas Nast, a radical Republican, later also used the donkey to represent a group of northern anti-civil war Democrats, and more generally as a symbol for pro-Democrat editors and newspapers.

By the end of the 19th Century, the symbol was firmly established.

Electoral College: The collective term for the 538 electors who officially elect the president and vice-president of the United States.

Presidential candidates require a majority of 270 college votes to win the presidency. The number of electors for each state is equal to the combined total of its senators and representatives in Congress.

The college system was conceived before the existence of political parties and was designed to allow the electors to act as independent voters. Electors are now expected to follow the wishes of the majority of voters in each state.

However, there have been a number of cases in recent elections where at least one elector has voted for a candidate other than the one they were pledged to. Two states, Nebraska and Maine, now divide their electors in proportion to the popular vote given to each candidate.

Elephant, Republican: The traditional symbol for the Republican Party, believed first to have been used in that context by an Illinois newspaper during Abraham Lincoln's 1860 election.

Thomas Nast popularised the image in a cartoon in a 1874 edition of Harper's Weekly, as pro-Democrat newspapers were accusing the Republican president of Caesarism for allegedly seeking a third term in office.

Emails (Clinton's...): While she was secretary of state from 2009 to 2013, Hillary Clinton relied on a privately hosted email server that handled all her personal and professional electronic correspondence.

The system became the centre of controversy in 2015 following confirmation of its existence and was the subject of hearings in Congress, public-interest lawsuits and an FBI criminal investigation that resulted in no charges being filed.

Around 50,000 of emails identified as work-related by Mrs Clinton's staff have been made public.

Correspondence deemed personal were permanently deleted, although the FBI has recovered around 17,000 emails from Mrs Clinton's servers, some of which its says are in the public domain.

Federal Election Commission (FEC): In 1975, Congress created the Federal Election Commission as an independent regulatory agency to administer and enforce federal election law.

The FEC discloses campaign finance information, enforces the law and oversees the public funding of presidential elections. By law, no more than three of the six members of the commission can be members of the same political party.

During an election period, the commission collects and publishes lists of contributions to all the official candidates, as well as their campaign spending.

Federal Election Campaign Act (FECA): First implemented in 1971, the Federal Election Campaign Act is a US federal law that provides for the disclosure of financial contributions to federal campaigns and regulates contributions.

In 1974, the law was toughened and new amendments established strict disclosure requirements for campaign donations, set specific limits for those donations, instituted public financing of presidential elections, and established the Federal Election Commission (FEC) to govern the whole process.

Subsequently, many of the restrictions on campaign spending and contributions have been pared back in a series of Supreme Court decisions.

Filibuster: A parliamentary technique of delaying a vote to pass legislation by giving a long speech.

In the Senate, it takes 60 votes to defeat a filibuster by ending debate on a bill.

In current practice, the minority party needs only to threaten a filibuster to block legislation, because the majority party typically holds less than the 60 votes needed to end debate on a bill and move to a final vote.

One of the most infamous uses of the filibuster came in 1957, when South Carolina Democrat Strom Thurmond gave a 24-hour tirade against a piece of civil rights legislation, in an ultimately unsuccessful effort to block it.

Founding fathers: An imprecise term used most often to describe those involved in drafting the Declaration of Independence from Britain in 1776 and the framing and adoption of the constitution at the Philadelphia Convention of 1787.

The term is sometimes also used to include influential figures in the struggle for independence and those who fought the Revolutionary War.

Front-loading: The tendency, which has become more marked in recent years, for states to move their primaries and caucuses forward, in an attempt to be among the first states holding a nominating contest.

State authorities believe that coming at the front of the queue increases their influence on the nomination process. However, if too many states hold their contests in a short space of time, critics argue, candidates are unable to connect with voters in each individual state.

A side-effect is that the process starts earlier in the year and is drawn out over a longer period.

Gaffe: A verbal error or slip-up made by a politician or other political figure. Or in a famous formulation by American journalist Michael Kinsley, a gaffe is when a politician accidentally says something he or she really means but that was better left unsaid.

Gerrymandering: The practice of drawing political constituency maps to increase a particular candidate's or party's advantage in a subsequent election.

In its rawest form, gerrymandering is when politicians choose their voters, rather than voters choosing their politicians.

In the US, political district maps are typically redrawn once a decade following the completion of the census.

The party in power in a state government uses sophisticated mapping and statistical data to redraw the map to ensure its candidates have the best chance of success, usually by diluting the electoral strength of the opposition party's supporters.

One mechanism might involve splitting a city into two or more House districts, each of which is then dominated by suburban voters.

Governor: The elected official of a state who is responsible for the effective and efficient workings of its government.

A governor's term of office lasts for four years. The number of times a governor can be re-elected varies from state to state.

Grand Old Party (GOP): The traditional nickname for the Republican Party widely used in American political reporting.

The party's official history traces the term back to the late 19th Century citing an article in the Boston Post headlined: The GOP Doomed.

The party website suggests the term may have evolved from the term used to refer to British Prime Minister William Gladstone - the Grand Old Man.

In Richard Nixon's 1964 presidential campaign, the GOP was used briefly as the basis for the slogan the "Go-Party", but by the late 1970s it had become firmly associated with the term Grand Old Party.

Hanging chad: A chad is the small piece of waste paper or card created when a hole is punched in a ballot.

Chads became famous in the 2000 presidential election, when the results in Florida were so close that a recount was necessary and electoral officials were forced to examine the ballot papers to determine voters' intentions.

Some voters had punched their preferences, but the chad had not fully separated from the ballot (a hanging chad).

In other cases, an indentation had been made in the ballot but it had not been punched through (a pregnant or dimpled chad).

Hard money: Money contributed by an individual directly to a particular campaign.

Individuals can currently contribute $2,500 to a candidate's primary campaign, and an additional $2,500 to a candidate's general election campaign. They can make these donations to multiple candidates.

The first $250 an individual donates to a candidate's primary campaign can be matched dollar-for-dollar from federal matching funds.

Limits on state-wide elections vary according to state laws.

The House of Representatives: The House is the larger of the two houses of Congress which are the law-making branches of government.

The 435 members of the House - generally known as Congressmen and Congresswomen - serve two-year terms.

The presiding member, the speaker of the house, is elected by a majority vote of members of the House at the beginning of each new Congress. In practice, this is the leader of the party holding the majority.

House members each represent approximately half-a-million citizens in their districts. The number of districts for each state is determined each decade by a proportional allocation based on the federal census.

House Majority Leader: The House Majority Leader is the second most powerful member of the majority party in the House of Representatives.

Unlike the speaker, he or she has no responsibility for the House as a whole, and focuses purely on advancing the interests of his or her party - for example, by organising members to support the party's policy agenda.

House Minority Leader: The leader of the minority party in the House of Representatives.

He or she acts as a spokesperson for the minority party's policy position and organises its legislative strategy.

In practice, the minority leader has very little legislative influence, because the House rules essentially allow the majority party to pass bills unilaterally.

Inauguration: The ceremony that marks the start of the new president's term of office. Under the US constitution, this happens on 20 January of the year following the election.

Independent: Registered voters who have not declared a party affiliation.

Because most voters registered for a particular party will vote for that party's candidate, general election campaigns have tended to focus on winning over these groups.

Nationwide about a third of all voters consider themselves independent, but some key states have a higher proportion of independent voters than others. New Hampshire, for example, traditionally has a large number of independents and as a result has a reputation for producing unexpected results during its primary elections.

Libertarian: A voter whose concerns are driven by belief in a small government, fierce support for fiscal conservative ideas and notions of individual liberty.

US libertarians tend to vote Republican, attracted to the party's advocacy for lower taxes and government spending and opposition to regulation of business and to the welfare state.

But many libertarians disagree with the party's stances on social issues and the war on drugs.

For example, while opposition to same-sex marriage is a key plank in the national Republican Party platform, staunch libertarian voters might argue the government has no business restricting two individuals' right to enter into a marriage compact.

In 2008 and 2012, libertarians have backed Ron Paul's candidacy for the Republican nomination.

Lobbyist: A person hired to represent the interests of a company, industry, political cause or foreign government in the Congress, regulatory agencies or other parts of the US government.

Effective lobbyists are very well-connected and are often former members of Congress or the Congressional staff or had other high-level jobs in the US government.

On the campaign trail, cosy connections with lobbyists - or worse, a background advocating for paid clients - can be a liability.

In the 2012 race, Newt Gingrich had to defend himself against allegations he took millions of dollars over the past decade to advocate on behalf of healthcare companies and a government-sponsored mortgage company.

McCain-Feingold: A 2002 campaign finance reform law named after its main sponsors, Republican Senator John McCain of Arizona and Wisconsin Democrat Russ Feingold.

The law was designed to limit the system of fundraising and corporate spending in federal election campaigns that existed outside the highly regulated infrastructure of public funding and hard money contributions to political candidates.

Much of the law was subsequently overturned by the US Supreme Court, which found restrictions on corporate spending in elections to be an unconstitutional infringement on freedom of speech.

Among the parts that remain intact are a ban on unlimited soft money donations to national political parties.

Medicaid: A health insurance programme for the poor and some disabled people that is funded jointly by the states and the federal government and administered at the state level.

It is up to states to determine matters of coverage, eligibility and the administration of the programme, but they must conform to broad federal guidelines.

Medicare: The national health insurance programme designed to help protect people aged 65 and over from the high costs of healthcare.

It also provides coverage for patients with permanent kidney failure and people with certain disabilities.

National convention: The party assembly held every four years at which state delegates from across the country gather to nominate the party's candidates for president and vice-president.

The nominees are typically chosen by party voters in primary elections and caucuses well ahead of the conventions, but the formal convention processes remain in place in case the decision over the party's candidate has to be brokered by the various party leaders.

In 1924, a bitterly divided Democratic Party took 103 ballots to decide on their presidential candidate.

Oval Office: The office traditionally occupied by the president in the West Wing of the White House.

The term is often used to describe the presidency itself, and the physical proximity of aides to the Oval Office is seen as reflecting the extent of their influence.

In addition to the Oval Office, the president keeps a private study next door.

Political Action Committee (Pac): An organisation formed to promote its members' views on selected issues, usually by raising money that is used to fund candidates who support the group's position.

Pacs monitor candidates' voting records and question them on their beliefs on issues of interest to their membership.

Because federal law restricts the amount of money an individual, corporation or union can give to candidates, Pacs have become an important way of funnelling large funds into the political process and influencing elections.

Pork barrel politics: The appropriation of government spending - or pork - pursued by a lawmaker for projects that benefit his or her constituents or campaign contributors.

Primary: A state-level election held to nominate a party's candidate for office. Regulations governing them and the dates on which they are held vary from state to state.

In some states, voters are restricted to choosing candidates only from the party for which they have registered support, however 29 states permit open primaries in which a voter may opt to back a candidate regardless of their nominal affiliation. In this case, strategic voting may take place with, for example, Republicans crossing over to back the perceived weaker Democratic candidate.

Primaries first emerged as a result of the so-called progressive movement of the early 20th Century, which argued that leaving the nomination process purely to party bosses was inherently undemocratic.

Pro-choice: The term used for those who support a woman's right to choose abortion if she so wishes.

Most pro-choice politicians will usually seek to avoid the emotive issue of abortion itself, following instead the libertarian line that government has no place interfering in what should be a private decision.

The Democratic Party has been broadly supportive of the pro-choice movement. President Bill Clinton summed up his party's stance by saying abortions should be "safe, legal and rare".

Pro-life: The term used to describe politicians and pressure groups opposed to abortion or allowing women to opt for abortion.

Some American advocates of the pro-life position believe abortion should only be allowed in cases where a pregnancy results from rape or incest. Others believe that abortion should be ruled out altogether.

The 1973 Roe v Wade decision by the US Supreme Court, which in effect legalised abortion in the US, is viewed by pro-life supporters as in contravention of the fundamental rights of the unborn child.

A more recent decision, Planned Parenthood v Casey in 1992, allowed states to limit access to abortion so long as they do not place an "undue burden".

Since then, conservative states have placed dramatic restrictions on abortion - for example, by enacting waiting periods between an initial consultation with the provider and the actual procedure, or by requiring doctors to inform pregnant women about the appearance and characteristics of the foetus.

Public funding: Money supplied to campaigns from government coffers and administered by the Federal Election Commission.

This includes primary election matching funds, which match the money candidates have raised privately, and a grant for the general election, and grants to fund the major parties' conventions.

Presidential candidates who accept public funding must agree to spending limits. In the general election, candidates who accept public funds may not raise private money in addition to the grant, nor can they spend more than the grant (though some legal and accounting expenses and some of candidates' personal cash is exempt).

In 2008, Mr Obama became the first candidate to decline public funds for the general election because he calculated he could raise more on his own and did not want to be held to a $84.1m spending limit - including what he had already raised privately. Also, he feared attack from well-funded independent conservative groups not subject to spending limits.

To qualify for primary election matching funds, candidates need to raise at least $100,000 in individual donations, including at least $5,000 from 20 different states.

Candidates who fail to receive at least 10% of the popular vote in two successive primary elections lose their eligibility for continued payments, unless and until they receive at least 20% of the vote in a later primary.

The two major parties - the Democrats and Republicans - are automatically entitled to a public grant to pay for the cost of their national conventions. Minor parties are also entitled to a smaller subsidy in proportion to the vote they received. New parties are not eligible.

Purple state: Another term for a swing state. A state which could vote Democratic (blue) or Republican (red).

Push polling: The controversial practice where voters are contacted over the telephone by people who are ostensibly taking a poll, but who talk up their own candidate and rubbish opponents.

Reagan Democrat: Working-class Democratic voter who defected from the party to vote for Republican candidate Ronald Reagan in the 1980 and 1984 presidential elections.

The term is also used these days to denote moderate Democrats who are more conservative than other Democrats on issues such as national security or immigration.

Red state: A state where people tend to vote for the Republican Party.

Roe v Wade: The landmark 1973 Supreme Court judgement that prohibited states from banning abortion.

The court's ruling was based on the concept that a woman's right to terminate her pregnancy came under the freedom of personal choice in family matters as protected by the Fourteenth Amendment.

The decision remains one of the most controversial ever made by the Supreme Court.

While states are prohibited from barring abortion outright, they have been allowed under subsequent Supreme Court rulings to restrict certain types of abortion and place often onerous requirements on doctors who provide abortion and women seeking them.

Running mate: The presidential nominee's candidate for the vice-presidency.

Second Amendment: The so-called right to bear arms amendment to the US constitution, ratified in 1791.

The text reads: "A well-regulated militia being necessary to the protection of a free state, the right of the people to keep and bear arms shall not be infringed."

The wording is open to interpretation and as a result it has become the focus of fierce debate between supporters and opponents of gun control.

Gun control opponents such as the National Rifle Association argue that the amendment gives Americans the constitutional right to bear arms free from any form of government control. But advocates of gun control argue the amendment was only written to guarantee the right to bear arms as part of a collective militia, and say states and municipalities should be able to restrict gun ownership and use.

Senate: The upper house of Congress, although members of the other house - the House of Representatives - traditionally regard it as an equal body.

The Senate has 100 elected members, two from each state, serving six-year terms with one-third of the seats coming up for election every two years. The vice-president serves as the presiding officer over the Senate, although he or she does not serve on any committees and is restricted to voting only in the event of a tie.

Senate Majority Leader: The leader of the majority party in the Senate, and the most powerful member of the upper house of Congress.

He or she controls the daily legislative programme and decides on the time allowed for debates.

Senate Minority Leader: The leader of the minority party in the Senate.

He or she acts as a figurehead for the minority party in the Senate, articulating its policy positions and attempting to deliver its legislative priorities.

Senator: Member of the Senate, the upper house of Congress. Each US state has two (a junior and a senior senator, distinguished by length of service).

Before Barack Obama, the last time a senator was directly elected to the White House was in 1960, when John F Kennedy won the presidency.

Speaker of the House: The leader of the majority party in the House of Representatives - not to be confused with the House Majority Leader.

The House Speaker has a dual role as both the leader of his or her party in the House, and as the presiding officer in the chamber, with responsibility for controlling debate and setting the legislative agenda.

Under the terms of the Presidential Succession Act of 1947, the speaker is the second in line to the presidency after the vice-president.

Stump speech: A candidate's routine speech outlining his or her core campaign message.

The speech can be tailored to suit specific audiences and may evolve over the course of the campaign.

The phrase stems from the days when candidates would make speeches standing on tree stumps. Campaigning politicians are still said to be on the stump.

Supermajority: The vote margin of two-thirds or three-quarters of the quorum, as opposed to a simple majority of 50% plus one.

For example, for an amendment to be added to the US constitution, it must be approved by a supermajority of two-thirds in both houses of Congress and the legislatures of three fourths of the states.

In the Senate, a supermajority of 60% is required to end a debate on a bill. In recent years, the minority party party has forced the senate to require a supermajority to pass almost all substantive legislation, contributing to political gridlock in Washington.

This gridlock is expected to be an issue in the 2012 presidential campaign, with Mr Obama and the Democrats accusing Republicans of using parliamentary manoeuvres to obstruct progress.

SuperPac: A category of independent political action group established by the Citizens United Supreme Court decision that is allowed to accept and spend unlimited amounts of corporate, individual or union cash on behalf of a candidate, often without disclosing its sources.

SuperPacs are barred from co-ordinating their spending - usually on advertising - with the candidates they support, but some say they in essence operate as shadow campaign committees. See entries on Citizens United and soft money.

Super Tuesday: The day in the campaign calendar, usually in February or early March of an election year, when a large number of states hold primary elections.

The first Super Tuesday occurred in the 1988 campaign, when southern state party officials hoped that by holding their votes on the same day they would increase the influence of the South and downplay the importance of the earlier New Hampshire primaries and Iowa caucuses.

Since then a number of other states have chosen to hold their primaries on the same day, including California.

Swing states: States in which the electorate is relatively evenly split between Republicans and Democrats, making them targets for aggressive campaigning by both sides.

In recent elections, the most important swing states were Florida, Ohio and Pennsylvania. Those have a high number of electoral votes, making them prime battlegrounds during the election.

The list of swing states changes with their demographics.

In the 2008 election, for instance, historically Republican Virginia and North Carolina voted for Barack Obama, anticipating their status as hard-fought swing states in 2012.

Others that were close in previous elections, like Iowa and New Mexico, appear to be solidly Democratic (see Battleground State).

Tea Party: A populist conservative movement known for its uncompromising stance on fiscal issues, its disdain for Mr Obama, and the stridency of its rhetoric.

The Tea Party movement arose in spring 2009 in opposition to Mr Obama's agenda, in particular his struggle to reform the US healthcare system.

Its primary demands are drastic cuts in government spending and taxes.

The movement's record of political success has been mixed.

Tea Party activists, supported with funding and organising assistance from well-heeled conservative backers, elected a class of fiscal conservative freshmen Republicans to the House of Representatives in 2010.

But their insistence on ideological purity has yielded some Republican candidates who are unpalatable to the broader electorate.

And Democrats blame the Tea Party movement for much of the Republican Party's inability and unwillingness to compromise on tax increases they say are needed to reduce the US budget deficit.

It is named after a series of colonial-era protests in which American revolutionaries dumped British tea into the sea to protest against a tea tax.

Third-party candidate: A candidate who does not belong to one of the two main US political parties, the Republicans or the Democrats.

Examples of third-party candidates who are running in 2016 are Libertarian Gary Johnson and Green Party's Jill Stein.

No third-party candidate has ever won the presidency, but may have influenced the result. In 1992, it's unclear if Ross Perot took votes away from incumbent George HW Bush and helped Bill Clinton to victory. In 2000, Green Party candidate Ralph Nader is believed to have siphoned votes from Democrat Al Gore.

Ticket: Usually preceded by the name of a party, the "ticket" refers to the candidates running together. Candidates for the presidency and vice presidency run on the same "ticket".

Trump University: A higher education institution founded by Donald Trump and two associates specialising in real-estate and asset-management education that operated from 2005 to 2010. It has been the subject of a New York state investigations for illegal business practices and two lawsuits alleging fraud. The legal proceedings are ongoing.

Vice-President: The presiding officer of the US Senate and the person who assumes the office of the president in the event of the resignation, removal, incapacitation or death of the incumbent president.

The vice-president only casts a vote in the Senate in the event of a tie.

Although those are the only duties the US constitution enumerates for the office, the vice-president can amass significant informal power in his capacity as an adviser to the president.

Early vice-presidents had little else in the way of official responsibilities.

In 1885 Woodrow Wilson, who would later become president, commented that there was "little to be said about the vice-president... His importance consists in the fact that he may cease to be vice-president".

In recent years, though, vice-presidents have taken on an increasingly prominent role managing a range of high-profile foreign and domestic policy programmes.

Dick Cheney, who served under George W Bush, is considered the most powerful vice-president in US history.

Wedge issue: An issue on which a candidate campaigns in order to divide factions within his opponent's supporter base.

For example, in 2004 Republicans proposed same-sex marriage bans in more than a dozen states and Republican candidates loudly trumpeted their support.

The subsequent referenda were aimed at attracting voters who support the Democrats on most economic issues but who feel strongly about social issues.

Conversely, Democrats might highlight their more liberal position on abortion, in an attempt to win over pro-choice Republicans.

Wonk: A political figure or pundit seen as having a studied and detailed command of public policy.