The X-ray (also called X-ray attack) is a tactical motif in which a piece exerts pressure through an opposing piece, targeting a valuable piece or square located directly behind it on the same line.
The key idea is that the attacking piece "sees through" the enemy piece standing in its way. If that intermediate piece moves or is captured, the target behind it is immediately exposed. For instance, a white rook on e1 facing a black rook on e4 and a black queen on e8 creates an X-ray threat: once the rook on e4 is removed from the line, the queen falls. This latent pressure — invisible at first glance — can force passive defensive moves or set up decisive combinations.
In practice, X-ray attacks appear most often in rook and queen endings, where heavy pieces operate along open files and ranks. Train yourself to spot alignments where your piece and an enemy piece "sandwich" a key target: recognising this threat early can win a pawn, force a favourable exchange, or even decide the game outright.