Checkmate (frequently shortened to mate) is a situation in chess (and in other boardgames of the chaturanga family) in which one player's king is threatened with capture (in check) and there is no way to meet that threat. Or, simply put, the king is under direct attack and cannot avoid being captured. Delivering checkmate is the ultimate goal in chess: a player who is checkmated loses the game. In normal chess the king is never actually captured – the game ends as soon as the king is checkmated because checkmate leaves the defensive player with no legal moves. In practice, most players resign an inevitably lost game before being checkmated. It is considered bad etiquette to continue playing in a completely hopeless position (Burgess 2000:481).
If a king is under attack but the threat can be met, then the king is said to be in check, but is not in checkmate. If a player is not in check but has no legal move (that is, every possible move would put the king in check), the result of the game is stalemate, and the game ends in a draw. (See rules of chess.)
A checkmating move is denoted in algebraic chess notation with the hash symbol (#) – for example, 34.Qh8# or by "++". (The symbol "++" is sometimes used to indicate double check.)
Read more about Checkmate: Examples, History, Two Major Pieces, Basic Checkmates, Rare Checkmate Positions