What is checkmate?
In Chess, the most valuable piece is the King. If you cannot get it
out of danger as described in the Check
Page, then it is Checkmate and
the game is over. To be checkmated the King has to be in check, and
have no way of getting out of the check.
Here are a few positions in which the black King is checkmated:
The King is threatened by the Rook here, and has no moves. By
looking carefully you will see that 3 possible squares are covered by his
own pawns, and the Rook covers the other squares. He is therefore checkmated.
The white Queen is defended by the King, and covers all escape
squares of the Black King, so it is checkmate.
The black King is in check by the Bishop and all his escape
squares are covered (shown by the arrows).