In chess, most pieces move consistently. Knights always move 2 spaces in one direction and another square sideways. Rooks always move along straight lines. Bishops can only move diagonally. Kings and pawns, however, can move in seemingly unorthodox ways.
The king’s special move is called castling. It involves moving the king 2 squares along the back rank and placing the rook that the king moved towards onto the square the king passed over.
In order to castle, several conditions must be met.
Both the king and rook must not have moved. Even if they return to their original squares, they cannot castle
The king cannot castle into, out of, or even through check. However, castling is still permitted if only the rook is under attack.
There must be no pieces between the king and rook
Kingside castling (castling short) is denoted as 0-0 and queenside castling (castling long) is denoted as 0-0-0.
Even without en passant, the pawn’s special move, it is unique in its movement. One of these attributes is that it can never go backwards or directly sideways. This means that 2 pawns beside each other usually can’t capture each other. The exception is that if a pawn moves 2 spaces forwards on their first move and lands beside an opposing pawn, the opposing pawn can capture the moving pawn as if it had only moved one square forward. This is the en passant move.
En passant can only be conducted on the move immediately after the first pawn move. It is denoted as a regular capture as if the captured pawn only moved one square. For example, the en passant capture is written as dxc3. (not dxc4)
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