Beginner
Cryptography
SHA-256
A widely used hash function producing a 256-bit (64 hex character) digest.
In simple terms
SHA-256 always outputs 256 bits, no matter how big or small the input is. Bitcoin uses it everywhere.
Analogy
A notary stamp that produces a unique, unforgeable reference for any document.
Going deeper
SHA-256 belongs to the SHA-2 family (Dobbertin, 2001): a Merkle–Damgård construction processing 512-bit blocks with six boolean functions and 64 round constants per block. Its 256-bit output gives a ~128-bit collision security margin under the birthday bound.
Common mistake
A common error is treating SHA-256 as encryption and expecting to "decrypt" a hash.