En passant (French: "in passing") is a maneuver in the board game of chess. The en passant rule applies when a player moves a pawn two squares forward from its starting position, and an opposing pawn could have captured it if it had only moved one square forward. The rule states that the opposing pawn may then capture the pawn as if it had only moved one square forward. The resulting position is the same as if the pawn had only moved one square forward and then the opposing pawn had captured as normal. En passant must be done on the very next turn, or the right to do so is lost. The move is unusual in that it is the only occasion in chess in which a piece captures but does not move to the square of the captured piece.
  
A pawn is captured en passant.
Historically, en passant is one of the last series of major rule changes in European chess that occurred in the 14th to 15th century, together with the introduction of the two-square first move for pawns, castling, and the unlimited range for queens and bishops. Because of their separation from European chess prior to that period, the Asian chess variants do not feature any of these moves.
The idea behind en passant was that when the two-square first move for pawns was introduced to speed up the opening phase, it was intended that time-honored defensive settings should not be invalidated by allowing pawns to sneak past opposing pawns.
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