Definition
A hash is the output of a hash function applied to input data. Cryptographic hash functions produce digests that are practical to compute but designed to make certain reverse or collision-finding tasks infeasible. The word can refer either to the resulting value or, informally, the hashing operation. It is not the same as encryption.
How It Works
The same input and algorithm produce the same digest. A small input change normally produces a substantially different result. Blockchains use hashes in transaction identifiers, block references, Merkle structures and proof-of-work processes. A verifier can hash a received file and compare the result with a trusted expected value to check whether the bytes match.
Key Considerations
A hash does not reveal a built-in way to decrypt the input. However, predictable inputs may still be guessed and tested, which matters for password handling. Since output space is finite, collisions are mathematically possible; security relies on making useful collisions difficult to find. Matching a published digest verifies consistency with that digest, not the trustworthiness of whoever published it.