A database that stores results of previously performed searches.

• It is a way to greatly reduce the search space of a chess tree with little negative impact.
• Chess programs, during their brute-force search, encounter the same positions again and again, but from different sequences of moves, which is called a transposition.

When the search encounters a transposition, it is beneficial to 'remember' what was determined last time the position was examined, rather than redoing the entire search again.

• For this reason, chess programs have a transposition table, which is a large hash table storing information about positions previously searched, how deeply they were searched, and what we concluded about them.

A transposition table makes uses of Hash functions to convert chess positions into an almost unique, scalar signature, allowing fast index calculation as well as space saving verification of stored positions.