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, which determine where the corresponding values are stored in an array. This enables quick access to data, typically in constant time, O(1), for operations like insertion, deletion, and lookup. When a collision occurs—meaning two keys hash to the same index—hash tables handle it using methods like chaining or open addressing. This structure is widely used in programming languages and applications, making it a fundamental concept in computer science and software development.