Key Square
A critical square in pawn endgames that, if occupied by the defending king in time, prevents the pawn from promoting.
Key squares are central to the "rule of the square" method for judging whether a lone king can catch a passed pawn before it reaches the promotion rank.
Etymology
Key comes from Old English cæg and from the beginning carried the figurative sense “solution, explanation, one who or that which opens the way.” Etymonline explicitly connects the adjectival sense “crucially important” (1913) to chess: it may be reinforced by “key move,” in chess problems, “first move in a solution to a set problem” (1827) — though that is the key move, not the key square. In endgame usage a key square is “a square whose occupation by one side's king guarantees the achievement of a certain goal, such as the promotion of a pawn,” also called a critical square. No source consulted gives an etymology, coiner, or first use for the square-specific term.
First documented: 1827 — Related concept “key move” in chess problems, attested 1827 (per Etymonline); the square-specific phrase itself is undated
Translations
Translations for this term haven't been added yet.