Threatening the capture of the enemy king such that it cannot escape. This wins the game for the attacking side.

An attack on the King where there is no way for your opponent to finish his turn and no longer have the King attacked. To be checkmated.

A position in which a player's king is in check and the player has no legal move (i.e. cannot move out of or escape the check). A player whose king is checkmated loses the game. Often shortened to mate.