What is a hash table?

A hash table is best defined as a collection of key-value pairs that employs a hash function to compute an index in an array, where the corresponding value can be stored or retrieved efficiently. The primary purpose of using a hash function is to ensure that each key is mapped to a unique index, which allows for rapid access to the stored values. This structure provides average-case time complexities for both insertion and lookup operations that are generally O(1), making it highly efficient for various applications, such as implementing associative arrays, database indexing, and caching.

In contrast, the other options describe different concepts that do not accurately represent a hash table. The definition involving a linear order pertains to data structures like arrays or linked lists, while sorting techniques deal with ordering elements rather than associating keys with values. Additionally, compressing data relates to reducing the storage size of information, which is unrelated to the fundamental purpose and operation of hash tables.