King and rook, one team move.

Move the king and rook together to improve king safety and rook activity, when the position allows it.

In standard chess, castling moves the king two squares toward a rook and brings that rook to the square the king crossed. Kingside: king e1 to g1, rook h1 to f1 for White. Queenside: king e1 to c1, rook a1 to d1. Black uses the eighth rank.