Inaccuracy

An inaccuracy is a move that makes the position somewhat worse than a stronger alternative. It may surrender a small advantage, miss a chance to improve a piece, or let the opponent reach a roughly balanced position, but it does not usually turn a reasonable position into a clearly lost one by itself.

The label is based on the change in evaluation, the judgment of which side stands better, between the played move and better options. There is no universal threshold. Platforms can use different formulas, and the importance of a change depends on actual winning, drawing, and losing chances. The same numerical shift may matter greatly in a balanced position and very little when the result is already nearly settled.

Learning from an inaccuracy requires more than memorizing the suggested best move. Identify the opportunity that was missed and the clue that could have revealed it. A mistake represents a more serious deterioration; the exact boundary between the labels depends on each platform's rules, not on an official law of chess.