What is Castling Short?

Castling Short, also known as castling kingside, is a special chess move where the king and the rook are moved at the same time. In this move, the king is moved two squares towards the rook on its initial square, then the rook moves to stand on the square the king has just crossed. This move is one of the few that allows two pieces to be moved in a single turn. Castling short can only occur under certain conditions, including that the king and involved rook have not previously moved, no squares between them are under attack, and no square that the king crosses is under attack.