A hash table is a data structure that stores key-value pairs, allowing for efficient data retrieval. It uses a hash function to convert keys into unique indices in an array, where the corresponding values are stored. This enables quick access to data, typically in constant time, O(1), for lookups, insertions, and deletions. However, collisions can occur when different keys hash to the same index. To handle this, techniques like chaining (linking entries at the same index) or open addressing (finding another open slot) are used. Overall, hash tables are widely used in programming for tasks like implementing dictionaries and sets.