A hash function is a specific kind of mathematical function that processes an input (or 'message') to produce a fixed-size string of characters, usually a hash value or digest that seems random. For each distinct input, the hash function will generate a unique output. It is computationally unfeasible to generate identical hash outputs from two disparate inputs, and it is also virtually impossible to reconstruct the initial input from its associated hash output.

Hash functions have various applications, such as verifying data integrity, securely storing passwords, and creating digital signatures.

In blockchain technology, hash functions are employed to create addresses, assemble blocks, and sustain the blockchain's structure and operation.