Queenside castling is a special chess move in which the king moves two squares toward the queenside — from e1 to c1 for White, or from e8 to c8 for Black — while the queenside rook moves to d1 (or d8 for Black), landing immediately to the king’s right.
For queenside castling to be legal, three sets of conditions must all be met: neither the king nor the queenside rook may have moved previously; all squares between them (b1, c1, and d1 for White; b8, c8, and d8 for Black) must be empty; and the king must not be in check, nor pass through or land on a square attacked by the opponent. Specifically, the squares the king crosses (d1/d8) and its destination (c1/c8) must be safe — but b1/b8 may be attacked without making the castling illegal.
In practice, queenside castling tucks the king behind its pawns, though the king often remains slightly more exposed than after kingside castling, since the a-file offers limited pawn cover. On the other hand, the rook immediately reaches d1 (or d8), pointing toward the center and becoming active at once. This is why queenside castling frequently goes hand in hand with dynamic, attacking play aimed at the center or the opponent’s kingside.