Special moves

A special move in which the king moves two squares toward a rook and that rook crosses to the king's other side.

Castling toward the kingside rook, leaving the king on g1 or g8 and the rook on f1 or f8.

Castling toward the queenside rook, leaving the king on c1 or c8 and the rook on d1 or d8.

A position state showing whether a player still retains the legal right to castle with each rook.

A pawn’s optional first move of two squares, legal only when both squares ahead are empty.

A special pawn capture that immediately takes a pawn just advanced two squares as though it had advanced one.

A temporary chance to capture an enemy pawn immediately after its initial two-square advance.

Promotion replaces a pawn that reaches the last row with a queen, rook, bishop, or knight of the same color.

The rank farthest from a pawn's starting side, where that pawn must become another piece.

A square on the farthest rank that a pawn reaches and must use to become another piece.

A queen, rook, bishop, or knight that replaces a pawn when it reaches the last rank.

Promotion in which a pawn reaching the farthest row is replaced by a new queen of the same color.

Underpromotion means promoting a pawn to a rook, bishop, or knight instead of choosing a queen.