1.Time in chess inwhich the King is being threatened, and cannot move anywhere else without being threatened again. This is the end of a chess game.

2. To win completely.

To turn up to a friend's house uninvited. Since you have travelled all the way there, they feel obliged to invite you in.

when you find yourself in a situation where you don't know what 'move' to try next when trying to get the attention of a person you fancy.

Office buddies who corner you into being their friends

when the minimal amount of urinals are used in a boys bathroom, but you cannot use one without breaking guy code

Checkmate is a position in Chess, in which a player's king is in a line of attack by an opponent's piece and cannot escape check. Thus, the attacking player wins the game.

Did you know that the quickest possible checkmate in Chess requires four moves only?

Although synonymous with "unbeatable", it can be used metaphorically to refer to anything you hold in high esteem.

Derived from the game of chess; checkmate is an offensive position in which the loser cannot move his/her king out of "check" (ie: imminent defeat).

Checkmate therefore means "unbeatable" with the implication that it is highly desireable to obtain.