The following is a list of electoral and political terms that frequently appear on the ElectionGuide and its component pages. Unless otherwise noted, definitions are adopted from World Encyclopedia of Parliaments and Legislatures (Washington, DC: Congressional Quarterly Inc., 1998).

Alternative vote (AV)

Single-winner voting system in which voters rank candidates in order of preference. If no candidate has a majority (or some other predetermined threshold) of first choices, the candidate with the fewest first choices is eliminated, and ballots cast for the eliminated candidate are reallocated to next-ranked candidates. Sequential eliminations continue until a winner emerges. Also known in the US as instant runoff voting (IRV), ranked choice voting (RCV); in Papua New Guinea as limited preferential voting (LPV - the voter gets up to three rankings); and generically as the single transferable vote (STV) applied to a single-winner election.

Apparentement

A pre-election grouping of parties permitting them to pool their vote totals for the purpose of meeting a threshold in a list proportional representation system. Parties preserve their separate identities on the ballot, and, within the apparentement, seats are allocated to each party in proportion to its vote share.

Block vote

See "multiple non-transferable vote."

Closed-list

A variant of list proportional representation in which voters do not directly influence the orders of candidates on lists. Party leaders typically determine these orderings.

Flexible-list

A variant of list PR in which the predetermined ordering of candidates (for purpose of seat allocation) prevails unless a candidate has received some quota of preference votes.

List proportional representation

Proportional electoral system in which seats are allocated to lists of candidates in proportion to each list's overall share of votes. For example, if a list is entitled to ten seats, the top ten people on its lists are seated. Lists may be open, closed, or flexible (see other definitions on this page). Different algorithms are used to determine how many seats a given list has won (e.g. d'Hondt, Hare, et cetera).

Magnitude

The number of seats allocated to a constituency. Frequently stated as "district magnitude" and, in mathematical contexts, as M.

Mixed-member majoritarian (MMM)

Describes a legislature of two or more tiers, one proportional and one non-proportional, in which seats in one tier are allocated independently of the distribution of seats by party in the other tier. Also known as a "parallel"  or "non-compensatory" system.

Mixed-member proportional (MMP)

Describes a legislature of two or more tiers, one proportional and one non-proportional, in which proportional representation seats are allocated to parties to reduce disproportion in the overall ratio of seats to votes. Proportional tier seats are allocated after non-proportional tier seats. Also known as a "compensatory"  or "personalized proportional representation" system. The latter term originates in Germany, where the single-member constituency tier is said to "personalize" a system of proportional representation.

Multiple non-transferable vote (MNTV)

A multi-winner voting system in which the voter may cast more than one but not more votes than the district magnitude (M), votes are not cumulative, and winners are the M candidates with the highest vote totals. When the voter has the same number of votes as the district magnitude, MNTV is colloquially known as the block vote or, in the United States, winner-take-all at-large. Known also as limited voting when the voter may cast more than one but fewer than M votes.

Open-list

A variant of list PR in which the order of a list (for seat allocation purposes) is completely determined by voters' preference votes. Voters may cast one or more preference votes. Preference votes frequently determine both lists' seat shares and the orderings of candidates on those lists.

Overhang seat

A seat that a party or coalition has won in the non-proportional tier of a mixed-member proportional system that is in excess of the number of seats to which it is entitled under whatever proportional allocation rule exists. Parties/coalitions may or may not be permitted to retain overhang seats.

Panachage

A feature of multi-winner electoral systems whereby voters have multiple preference votes, which they may distribute among multiple candidate lists. Usually used in reference to open- and flexible-list PR systems, but nonetheless logically consistent with MNTV systems.

Proportional representation (PR)

(1) Describes a situation in which the ratio of seats by party to votes by party approximates one-to-one. (2) A family of electoral systems intended to deliver the above result (at the constituency level).

Single non-transferable vote (SNTV)

Multi-winner voting system in which the voter may cast one vote. Winners are the M candidates, where M represents district magnitude, with the highest vote totals. In the United States, the one-vote variant of limited voting.

Single transferable vote (STV)

A multi-winner voting system originally designed to minimize wasted votes and deliver proportionality of seats to votes. Voters rank candidates in order of preference. Winning candidates must achieve quotas or victory thresholds of votes, which depend on district magnitude. Votes for candidates in excess of the threshold (i.e. surplus) are transferred to next-ranked candidates. When no candidate has a surplus of votes, the candidate with fewest votes is eliminated, and votes for that candidate are transferred to next-ranked candidates. This process continues until all seats are filled. Also known in Australia as the Hare-Clark system, colloquially as "preference" or "preferential voting," and in the United States as choice voting or ranked choice voting. Methods of surplus transfer vary by jurisdiction (e.g. fractional transfer, random transfer, Cincinnati method, et cetera).

Tier (legislative)

Legislatures can be conceptually divided into groups of seats called tiers. Each tier is defined by a feature of interest in the respective set of electoral rules. In mixed-member systems, for example, one tier may be elected in single-seat constituencies, and another tier may be elected under list proportional representation.

Two-round system (TRS)

An electoral system in which the failure of some candidate(s) to receive a predetermined quota of votes triggers a second round (i.e. runoff) on a later date. TRS are typically used for single-winner elections, the quota is typically an absolute majority, and only the top two candidates from the first round typically compete in the second round. Often called "majority system."

Wasted vote

A vote that does not contribute to the allocation of a seat to a winner, whether cast for a losing candidate or for a winner who has enough votes to win already.