En passant
French for 'in passing'
A special pawn capture of a pawn that just advanced two squares, as if it had moved only one.
If your pawn is on its fifth rank and an enemy pawn on an adjacent file advances two squares in one go, landing beside yours, you may capture it as though it had moved a single square — but only on the very next move.
It exists so the two-square first move cannot be used to sneak a pawn past an enemy pawn that would otherwise have blocked it.
It is the rule most casual players forget exists, and it decides real endgames and tactics.
Assuming a pawn 'escaped' by moving two squares — sometimes it can be taken en passant, sometimes you must take it immediately or lose the right.
Related terms
See En passant in your own games
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