- An abbreviation used here for the Conservative Party
- A parliamentary constituency is a defined local area whose residents elect one Member of Parliament, to one House of Commons seat.
- The electorate comprises all those people who are registered to vote at an election.
House of Commons seat
- The UK House of Commons has, at each election, a fixed number of seats (one seat per parliamentary constituency). At the time of the 2005 election there were 646 seats; by May 2010 some constituency boundaries had been re-drawn, and the number of seats was 650.
- The outcome of a general election is a hung parliament if no single political party has a majority.
- An abbreviation used here for the Labour Party
- An abbreviation used here for the Liberal Democrat Party
- A political party has a majority in the House of Commons if its members occupy more than half of the seats. The size of the majority is the difference between the majority party's number of seats and the total number of seats held by all other parties.
- The well-established polling company now known as Ipsos MORI
- The well-established polling company nowadays known as GfK NOP Market Research
- A panel study is a statistical survey which seeks responses repeatedly, at separate points in time, from the same respondents. Usually the objective of such a survey is to study change through time. In the exit-polling context as described here, the panel "members" are polling stations, and the "points in time" are successive elections.
- A polling station is a place where registered electors from the local neighbourhood may go to cast their vote on the day of the election. Polling stations are often in schools or village halls, for example. Each parliamentary constituency has many polling stations, at different locations.
- Some electors are registered to vote by post (mail) rather than by visiting a polling station in person on the day of the election. The number of people registered to vote by post in the UK has been steadily increasing in the last few years, and is currently around 20% of the electorate. This is a potential source of bias in predictions made from exit polls.
- Some electors who are selected for inclusion in the exit poll refuse to cooperate with the interviewer. This is a potential source of bias in the results.
- An abbreviation used here for the Scottish National Party
- The Speaker of the House of Commons is a Member of Parliament who is elected by the House to preside over its affairs. By convention, if the sitting Speaker wishes to continue in that office after a general election, the main political parties do not contest the Speaker's seat.
- As used here, the word statistics means the art and science of drawing reliable conclusions from uncertain data.
- Definition of Steed swing to appear here
- The swing — or Butler swing — from party A to party B between successive elections is calculated as the average of the increase in B's share of the vote and the decrease in A's share of the vote. It is usually expressed in percentage points. If the shares are calculated as fractions of only the votes cast for A and B, the result is known as Steed swing.
- When an elector strongly prefers party A to party B but perceives that A has no chance of winning in their local constituency, that elector might vote for a third party C if C is perceived to have a substantially greater chance of defeating B. Votes cast in this way are said to be tactical. (That's the UK terminology: elsewhere it might be called strategic voting.)
- The turnout at an election is the fraction of the registered electorate who actually voted.