A hash table is a data structure that stores data in an associative manner, where each data value has its own unique index value. It is also known as a hash map and is used to implement an associative array, which is an abstract data type that maps keys to values. A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired value can be found. During lookup, the key is hashed, and the resulting hash indicates where the corresponding value is stored.

The performance of a hash table is dependent on the hash functions ability to generate quasi-random numbers for entries in the hash table. If the hash function generates the same hash for distinct keys, this results in a collision, which is dealt with in a variety of ways. Hash tables can be used to implement caches, auxiliary data tables that are used to speed up the access to data that is primarily stored in slower media. They are widely used in many kinds of computer software, particularly for associative arrays, database indexing, caches, and sets.

In summary, a hash table is a data structure that maps keys to values using a hash function to compute an index into an array of buckets or slots. It is used to implement associative arrays, database indexing, caches, and sets, and is widely used in many kinds of computer software.