Tempo

A tempo is the smallest unit of time in chess. One side moves; that is one tempo. Whoever can do useful work without their opponent doing equally useful work in reply has gained a tempo. The accumulation of tempi over an opening or a tactical sequence is often the difference between equality and a decisive advantage.

A move that develops a piece while threatening something — forcing the opponent to defend — gains a tempo. The opponent’s reply is forced; it does not improve their position. Meanwhile, the attacker has improved theirs. This is why active threats in the opening matter: not because they win material directly, but because they buy time.

A move that wastes time — moving the same piece twice, retreating, repeating a position — loses a tempo. The opponent uses the unanswered turn to develop or to threaten something. Over five or six moves, a single tempo lost can become a clear disadvantage.

In the endgame, tempo often means something very specific: who has the move in a position where moving is bad. A king-and-pawn endgame can turn on which side has to move when both kings are in opposition. The side that has to move loses the position; the side that does not is said to hold the tempo or have triangulated correctly. See also: zugzwang, triangulation.