What is Castling Short?

Castling short (or kingside castling) is the form of castling in which the king moves two squares toward the h-file rook. Notated as O-O. The king lands on the g-file and the rook on the f-file. Kingside castling is more common than queenside castling because the king is typically better sheltered behind the f-, g-, and h-pawns.