A plurality (or "relative majority") is the largest share of something. Depending on the definition used, a majority may or may not also be a plurality, though note that a plurality isn't always a majority. Some elections or types of votes require merely a plurality, while others require a runoff to produce a majority.
The term plurality is also often used to categorize voting methods that operate by looking mainly at voters' 1st choices. Choose-one FPTP voting and STV fall into this category, as do the plurality-runoff voting methods.
For example, if there are three candidates A, B, and C, with A having 40% of the votes, B 30%, and C 30%, then A has a plurality (more votes than all others), but not a majority (which would be at least 50% + 1).
NotesSeveral voting methods attempt to represent a majority, rather than only a plurality, of voters. Category:Graded Bucklin methods are prominent for this. Yet this can lead to situations where the plurality of voters suffer Later-no-harm violations to satisfy only slightly more voters; example:
51 A>CIf C doesn't run, then A wins by the majority criterion. But with C in the race, A is only a plurality's 1st choice, and C wins in Bucklin. Yet if A-top voters bullet vote, then they guarantee A wins in any voting method passing the Plurality criterion. Thus, attempting to avoid plurality-supported candidates can have odd effects. One way to get around this is to focus on majorities in the pairwise context, rather than absolute majorities, as this would show A to be the Condorcet winner in the above example.
49 B10 C