Definition:Chess/Rules/Capture/Pawn/En Passant

Definition
En passant pawn capture is a method by which a chess pawn may capture a pawn of the opposite colour in particular circumstances.

Let pawn $a$ be on the player's $5$th rank.

Let pawn $b$ be of the opposite colour to pawn $a$.

Let pawn $b$ be on its starting position, on one of the files adjacent to the one occupied by pawn $a$.

Let pawn $b$ move forward $2$ spaces, in the process crossing over one of the squares which is under attack from pawn $a$.

Then pawn $a$, on its next move only, may move into that square crossed over by pawn $b$, and capture pawn $b$ "while it is passing".

This mode of capture is known as capture en passant.

In the above diagram:


 * the black pawn on $\text b 7$ moves forward to $\text b 5$


 * the white pawn on $\text c 5$ then moves to $\text b 6$, while capturing the black pawn which is actually on $\text b 5$.

The board then looks like this: