end of a match; end of a game
Used in sports and competitive contexts to announce or refer to the conclusion of a match or game.
The whistle signaling the end of the match sounded.
There are five minutes left until the end of the game.
試合終了 is the neutral, formal term for the end of a match used in official contexts, while ゲームセット is a more colloquial, dramatic wasei-eigo phrase shouted to announce the same moment.
Compound of 試合 (match, game) and 終了 (end, conclusion).