Checkmate is the winning move in chess that ends the game. When you put your opponent's king in checkmate, the king is under attack (in “check”) and has no way to escape: it can't move to safety, no other piece can block the attack, and no piece can capture the threatening piece. Game over.

The word comes from Persian, where shah mat meant “the king is helpless” or “the king is defeated.”

In chess, you might threaten your opponent's king many times during a game by putting it in check, forcing them to respond. But checkmate is different: it's the moment when there's nowhere left to run. A player might see checkmate coming several moves ahead and resign rather than play it out, like a mathematician who spots an unsolvable problem.

People also use checkmate outside of chess to describe any situation where someone has been completely outmaneuvered with no options left. If your sister proves you wrong with unbeatable logic, she might joke that she's checkmated you. Unlike chess, though, most real-life problems have more than one solution.