Pin — what it means in chess
An attack on a piece that cannot move without exposing a more valuable piece behind it.
An attack on a piece that cannot move without exposing a more valuable piece behind it.
A pin freezes a piece in place. It is attacked, but if it moves, something more valuable behind it is exposed — so it cannot move, or will not. When the piece behind is the king, the pin is absolute and the pinned piece is legally stuck. When a queen or rook sits behind instead, the pin is relative: moving is legal but costly. A pinned piece is a piece that has stopped defending, which is why pins win material a move later as often as they win it outright.
A pin does its work quietly. The pinned piece looks fine on the board, but it has stopped doing its job: it is no longer defending the squares it used to cover, no longer available to move where it would like to, and no longer a real piece from your opponent's point of view. That is why so many tactics show up a move after the pin, not on the pin itself — attack the pinned piece a second time, and it cannot be defended by moving. The classic follow-up is a pawn push (h3, g4) to kick the pinning bishop away or trade it off, but sometimes the right idea is to leave the pin in place and pile pressure on the frozen piece.
[[board startfen="rnbqkb1r/ppp1pppp/5n2/3p4/3P4/5N2/PPP1PPPP/RNBQKB1R w KQkq - 2 3" pgn="3. Bg5" caption="A relative pin: the f6 knight can't move without losing the queen on d8 behind it." notes="White to move, with the bishop ready to come out. Bg5 pins the knight on f6 to the queen on d8. The knight is attacked, but if it moves, the queen falls — so for now it is stuck, defending nothing."]]
The Endgame Society glossary defines more than 240 chess terms — rules, notation, tactics, strategy, pawn structures, endgames, and openings — in language a beginner can act on rather than dictionary shorthand.