What is a function that maps data of arbitrary size to data of a fixed size?

A hash function is a specific type of function that takes input data of arbitrary size and produces a fixed-size output, often referred to as a hash value or hash code. The primary purpose of a hash function is to uniquely represent data in a way that is efficient for storage and comparison.

Hash functions are widely used in computer science, especially in areas like data structures (e.g., hash tables), cryptography, and data integrity verification. When data is hashed, even a small change in the input will produce a significantly different hash output, which aids in detecting alterations to the data.

This characteristic of mapping varying input sizes to a consistent output size makes hash functions highly valuable for creating indexes, checksums, and digital signatures, among other applications. In contrast, other options mentioned do not have the same focus on transforming arbitrary input sizes into fixed-size outputs.