Hashing is a technique to map data of arbitrary size to fixed-size values, and hash tables use hashing to efficiently store and retrieve data based on keys.

Hashing is a fundamental concept in computer science that involves transforming input data of varying sizes into fixed-size values, known as hash values or hash codes. This technique is particularly useful for efficient data retrieval and storage, allowing for fast access to data through a unique identifier (the hash). The process of hashing employs a hash function, which takes an input (or key) and produces a hash value that typically represents the index of an array where the associated data will be stored.

A hash table is a data structure that utilizes hashing to maintain key-value pairs, offering average-case time complexity of O(1) for search, insertion, and deletion operations. In a hash table, keys are transformed into hash values, which are then used as indices in an array to store the corresponding values. This structure enables quick lookups and modifications, making hash tables ideal for scenarios that require fast access to data, such as implementing dictionaries, caches, and sets.

However, hash tables are not without challenges. Collisions can occur when two different keys produce the same hash value, leading to the need for collision resolution techniques, such as chaining (where multiple elements are stored in a linked list at the same index) or open addressing (where a probing method is used to find the next available slot). Understanding hashing and hash tables is essential for optimizing data access patterns and effectively managing large datasets in various applications.