\begin{definition}[Definition:Chess/Rules/Capture/Pawn/En Passant]
'''''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'''''.
{{ChessDiagram|
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|  |ul|  |  |  |  |  |   
|  |da|pl|  |  |  |  |  
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}}
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:
{{ChessDiagram|
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|  |  |  |  |  |  |  |  
|  |pl|  |  |  |  |  |   
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}}
\end{definition}