A single-winner rule under which the candidate with the most votes wins, even without a majority. Often called first-past-the-post.
In more detail
Each voter marks one candidate. It is used for House of Commons elections in the UK and in most US congressional elections. With three or more serious candidates, the winner may lack majority support, and similar candidates can split votes. Duverger's 'law' says plurality voting in single-member districts tends to produce two-party competition; scholars treat it as a strong tendency, not an iron law. Alternatives include runoffs, ranked-choice voting and approval voting.