Check, Checkmate, Stalemate. These chess terms are used in everyday conversation -- here's what they mean.
During a normal game of chess, a player attacks the opponent's pieces many times. Usually the opponent will beat off the attack by moving the attacked piece, by capturing the attacker, or by intersecting the line of the attack. Sometimes a player will ignore an attack on a piece when, for example, there is a counterattack of greater value.
There is one attack that can never be ignored -- an attack on the King. Simply put, you can't leave your King under attack. If you have no way of escaping the attack, you lose the game.