Stalemate
A stalemate is when a chess player's King is not in check, but the player still cannot make any valid move (chiefly because doing so would put their King in check).
A stalemate results in a draw (although historically this rule has evolved through pretty much every permutation you can imagine). It's therefore important to ensure you checkmate, rather than stalemate, your opponent.
Outside of chess, when used as a metaphor, the phrase "stalemate" seems to be used as if synonymous with "standoff", suggesting that neither player can make a valid move. This is quite different to its actual meaning when playing chess, which only requires a single player to be unable to move. Double stalemates, in which neither player can move, are extremely rare.
Chess rules: Check | En passant | Stalemate
