swing vote

A swing vote is a vote that moves or may move from one political party or candidate to another, usually in one election cycle.

It consists of those disaffected with their current political choice, those that may not vote at all if they see nothing they think it uniquely worth voting for, and those easily swayed at the last minute to change their vote or "send a signal".

A tactical vote is by some definitions a swing vote, as it has no potential to move at the last moment unless it is up for rational argument and persuasion. However a true swing vote reflects a desire for a positive choice, not a rejection of a bad outcome. See tolerances versus preferences.