wasted vote; vote for a losing candidate
Refers to a vote that does not contribute to electing a candidate, typically because it was cast for a losing candidate or is otherwise ineffective under the electoral system.
Under a single-seat constituency system, wasted votes tend to increase.
His vote ended up being a wasted vote.
Compound of 死 (death, dead) and 票 (vote, ballot), literally 'dead vote'. The term is a modern political-science coinage.