zugzwang

Zugzwang is a term used in chess and other strategy games to describe a situation in which a player is at a disadvantage because any legal move would worsen their position. The constraint is that it is the player's turn to move, and passing is not allowed; every available move harms the player's prospects, often leading to a loss or a forced concession.

The term is German, literally meaning move-impulse or compulsion to move; Zug means move and Zwang means compulsion. It entered chess vocabulary in the late 19th century and has since become a standard concept in instructional material and game analysis.

In chess, zugzwang most commonly arises in endgames and simplified positions, where one side's only moves enable the opponent to gain a decisive tempo or to promote a pawn. A pure zugzwang means every legal move worsens the position; the player to move would prefer to pass, if such a pass were allowed.

The idea is also applied to other two-player, turn-based games with perfect information, such as checkers or Go, and to endgame studies and computer chess, where locating zugzwang sequences helps explain why certain positions are losing despite apparent material balance. Recognizing zugzwang can shape strategic planning, as forcing the opponent to move can be a decisive weapon in tight positions.