Definitions: X-Ray Attack

Looks similar to, but is distinct from pinning (see previous post).

X-Ray Attack: A higher value piece is attacked. If it moves, a lower value piece on the same line is exposed to attack.

Reinfeld Position #757
White to move

White plays 1. Rh8 a pawn promotion threat, 1. ... Rxa7 2. Rh7+ when the King moves, the X-Rayed Rook is captured.