En passant

En passant (From french: In passing) a special form of capture known almost entirely from Orthochess and games derived from it. In Orthochess, it applies only to pawns and can only occur immediately after a pawn moves two ranks forward from its starting position and an enemy pawn could have captured it had the pawn moved only one square forward (the capturing pawn must be on its fifth rank prior to executing this maneuver). The opponent captures the just-moved pawn "as it passes" through the first square. The resulting position is the same as if the pawn had moved only one square forward and the enemy pawn had captured it normally.