key terminology; electoral systems

Minority Government

A government that enters office but which does not have a majority of seats in the legislature (Parliament). This makes passing legislation very difficult.

Coalition Government

A government that is formed of more than one political party. It is normally accompanied by an agreement over policy options and office of state, as was the Conservative-Liberal-Democrat coalition from 2010-2015

Additional Member System (AMS)

A hybrid electoral system that has two components or elements. The voter makes two choices. Firstly, the voter selects a representative on a simple plurality (FPTP) system then a second vote is apportioned to a party list for a second or 'additional' representative

Marginal Seat

A seat held by the incumbent with a small majority. There is no precise percentage or winning margin to which this aligns but a 10% margin would need only a swing of 5% to the rival party to take it. Marginal seats are important as they are where the outcomes of elections are decided. Only a minority of seats in UK Westminster constituencies are marginal.

Safe Seat

A seat in which the incumbent has a considerable majority over the closest rival and which is largely immune from swings in voting choice. The same political party retains the seat from election to election. A majority of seats in UK Westminster constituencies are safe seats.

First-Past-The-Post (FPTP)

An electoral system where the person with the most number of votes is elected. Victory is achieved by having one more vote than other contenders - it is also called a plurality system.

Supplementary Vote (SV)

This is a majoritarian system. The voter makes two choices (hence the term 'supplementary'). If one candidate obtains over 50% on the first vote then the contest is complete, if no candidate attains this level, all but the top two candidates remain. Then the supplementary choices are re-distributed and whoever gets most votes from the remaining two, wins the seat.

Single Transferable Vote (STV)

This system allows voters to rank their voting preferences in numerical order rather than simply having one voting choice. In order to obtain a seat, a candidate must obtain a quota. After the votes are cast, those with the least votes are eliminated and their votes transferred and those candidates with excess votes above the quota also have their votes transferred.