Questions relating to checkmating.
In standard chess, a checkmate is the only way to win a game (other than resignation of the game by a player). Checkmate occurs when a King is attacked (i.e. threatened to be captured on the next move) by an opposing piece (attack against the King is called check), and the only moves available to the attacked player cannot remove the King from check. In such a case, the attacked player is said to be checkmated, and the other player wins the game.
The word checkmate comes from the Persian phrase "Shāh Māt," which translates literally as "the king is helpless." For more on the history of the notion of checkmate, see this Wikipedia entry.