[from French, "in the act of passing"] The rule that allows a pawn that has just advanced two squares to be captured by an enemy pawn that is on the same rank and adjacent file. The pawn can be taken as if it had advanced only one square. Capturing en passant is possible only on the next move.

Capturing a pawn that moved 2 spaces with a pawn that could have captured it if it had only moved 1 space, on the next turn only.

French "in passing." It occurs when a pawn moves two squares from its starting position, and passes an enemy pawn that has advanced to its fifth rank. The advanced pawn on the fifth rank may choose to capture the pawn as if the pawn had only moved forward one square. This capture must be made immediately after the two square advance, or else the right to capture "en passant" is lost. In chess notation an en passant capture is labelled "e.p."