X-ray — what it means in chess
A piece acting through an enemy piece on the same line.
A piece acting through an enemy piece on the same line.
An x-ray is an attack or defense that operates through an enemy piece. The piece in the middle blocks the line for now — but if it ever moves, captures, or is captured, the power behind it lands on the far square as if it had been there all along. The x-ray is the tactic of latent force: what a rook sees through another rook is not blocked, only delayed.
[[board startfen="6k1/4P1pp/8/4r3/8/8/8/4R1K1 w - - 0 1" pgn="1. e8=Q+ Rxe8 2. Rxe8+" caption="X-ray support: the rook guards e8 through the enemy rook, and cashes on the recapture." notes="White to move. The e7 pawn stands one step from promotion, and the Black rook on e5 seems to control the queening square. But the White rook on e1 sees e8 too — through the Black rook. e8=Q+ — the pawn promotes anyway, with check. Rxe8 — Black captures the new queen, exactly as planned. Rxe8+ — and the x-ray cashes. The rook that seemed blocked recaptures through the vacated file: pawn and queen traded away, a full rook collected, with check."]]
The x-ray is the skewer's quieter sibling — a skewer attacks through a piece that must move, while an x-ray works through a piece that merely might. It also powers the sneakiest defenses in chess: a back rank that looks loose but is guarded through an enemy rook is not loose at all. Related in geometry, if not in temperament: the pin.
The Endgame Society glossary defines more than 240 chess terms — rules, notation, tactics, strategy, pawn structures, endgames, and openings — in language a beginner can act on rather than dictionary shorthand.