Pin, Fork, Tempo, Fork

In chess, a pin is a chess tactic in which a defending piece cannot move without exposing a more valuable defending piece on its other side to capture by the attacking piece. Moving the attacking piece to bring on the pin is called pinning; the defending piece so restricted is described as pinned.

In the position from this morning's game, the pawn on e4 is pinned to the King by Black's Queen. This is called an absolute pin, because the pinned piece absolutely cannot move out of the pin as it is illegal to move into check.

A fork is a tactic in which one attacker puts two targets in danger at the same time. A tempo in chess a tempo is a "turn" or single move (a half-move or ply made either by White or Black). A tempo can be gained by a check or an attack on an undefended piece or a piece of greater value.

In this case, Black can unleash a tempo gaining fork by attacking the pinned piece, followed by a second fork on the subsequent move.