A hash table, also known as a hash map, is a data structure that allows for fast data retrieval by mapping keys to values using a hash function. The hash function computes an index for each key, which determines where the corresponding value will be stored in the table. This allows for constant time complexity (O(1)) on average for operations like insert, delete, and lookup, making hash tables one of the most efficient data structures for storing and retrieving data. In TypeScript, you can implement hash tables using objects or the `Map` class, both of which allow you to store key-value pairs. The primary difference between hash tables and arrays is that hash tables provide faster lookups when the data is stored using a non-numerical key, such as strings. However, hash tables are prone to collisions, where two different keys produce the same index. To handle collisions, hash tables use techniques such as chaining (where multiple values are stored in a list at the same index) or open addressing (where the table searches for the next available index). Hash tables are widely used in scenarios like caching, symbol tables in compilers, and implementing associative arrays or dictionaries. Mastering hash tables is crucial for solving problems that require fast lookups and efficient data storage.