casting vote; deciding vote
A vote that breaks a tie or decides an issue when other votes are evenly split. Used in formal meeting or election contexts.
It was passed by the chairperson's casting vote.
A loanword from English 'casting vote', often used in political contexts. 決定投票 is the native Japanese equivalent and is more common in formal written Japanese.
Compound of 決定 (decision) and 投票 (vote).