additional member system (AMS) See mixed-member proportional system (MMP).
alternative vote (AV) A majoritarian system using preferential voting and typically based on single-member districts. Voters rank candidates in order of preference. If no candidate gains over 50 per cent of first preferences, the last-placed candidate is eliminated and the second preferences of his or her supporters are distributed; this is repeated until a candidate passes 50 per cent. In Australia and New Zealand, this is known as the preferential voting system. In the US, it is known as instant runoff voting (IRV).
block vote (BV) A plurality system using multi-member districts. In a district electing m members, voters can vote for m candidates. Votes for candidates are added up and the m top candidates are elected. For a variant, see party block vote.
bonus-adjusted system (BA) Any system in which the distribution of seats determined by the main electoral system is adjusted by the allocation of a bonus to one or more parties. This bonus may constitute a fixed proportion of the total seats or it may be a variable number designed to ensure, for example, that the largest party secures a specified minimum overall share.
Borda count (BC) A preferential system in which candidates score points according to their position in voters' rankings. In the simplest form, supposing there are four candidates, a voter's first-choice candidate receives four points, their second choice three points, and so on.