A hash table is a data structure that stores key-value pairs, allowing for fast data retrieval. It uses a special function called a hash function to convert keys into unique indices, which determine where the corresponding values are stored in an array. This makes searching for data very efficient, as it can often be done in constant time, O(1). When a collision occurs—meaning two keys hash to the same index—the hash table uses techniques like chaining or open addressing to resolve the issue. This ensures that all data can be stored and accessed without losing any information, making hash tables a popular choice for implementing data dictionaries and caches.