Quiescence search is Stockfish’s method to avoid evaluating “noisy” positions—positions with pending captures, checks, or tactical threats—because static evaluation is unreliable when the position is unstable. Instead of stopping the search at the leaf node, the engine extends the search further but only along tactical moves like captures, promotions, and sometimes checks. This continues until the position becomes “quiet,” meaning no immediate tactics are available, and only then is the NNUE/static score used. Without quiescence search, engines would suffer from the “horizon effect,” missing tactics just beyond the search boundary.