What does castling mean?
Castling is a special defensive maneuver in the game of chess, and the only legal move in which a player moves two of their own pieces in a single turn. To castle, the king slides two squares along its back rank toward one of its rooks, and that rook simultaneously leaps over the king to occupy the adjacent square. The move serves chiefly to shelter the king behind a wall of pawns while bringing the rook toward the center of the board, so players often speak of castling 'early' to secure their king before launching an attack. There are two forms: kingside castling (with the rook nearer the king) and queenside castling. Because it can be performed only once per game and under strict conditions — both pieces must not have moved, no pieces may intervene, and the king may not pass through check — knowing when to castle is considered a fundamental skill for every chess player.
A special chess move in which the king moves two squares toward a rook and that rook moves to the square the king has crossed, all in one turn.
"Beginners are taught to aim for castling within the first ten moves."
Kingside castling is denoted O-O in algebraic notation; queenside castling is O-O-O.
(Present participle/gerund of 'castle') To perform this move; to protect one's king by moving him behind his own pawns using the castling maneuver.
"After castling early, White could focus on developing the rest of the army."
Rarely pluralized; the singular is almost always used even when referring to multiple instances of the move across games.
"Both castlings occurred within the opening phase of the game."
Castling is the only move in chess where you get to move two pieces in a single turn — and it's been part of the game for over 500 years.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of castling
The word castling derives from 'castle', which comes via Old French 'chastel' from Latin 'castellum', a diminutive meaning a fortified place or small fort. The chess term arose because early European versions of the game depicted the rook as a tower or castle, so the king-and-rook maneuver came to be described by that piece's name. Cognates include French 'château' and the English derivatives 'castellan' and 'castellated'.
Related word forms
How castling is actually used
Almost exclusively used in chess contexts. In standard chess notation, kingside castling is written 'O-O' and queenside castling 'O-O-O'. A player may only castle if neither the king nor the rook involved has moved previously, if no pieces stand between them, if the king is not in check, and if the king does not pass through or land on an attacked square.
Easily confused with castling
A castle is the fortified building itself, whereas castling is specifically the chess maneuver involving the king and rook.