en passant

In passing, by the way, incidentally.

Of a capture of an enemy pawn, by moving one's pawn to the square that the enemy pawn has just passed over.

Of a capture, performed by a pawn on an enemy pawn that has just passed over its attack zone.

A move in which a pawn captures an opposing pawn on the same rank immediately after the latter has moved forward two squares on its first move in the game, as if it had moved forward only one square.