Bitcoin’s SHA-256 hash function belongs to the SHA-2 family.
SHA-2 is a family of cryptographic hash functions designed by the United States National Security Agency and first published in 2001. Its members include SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and SHA-512/256; the number identifies the digest length in bits.
Bitcoin uses double SHA-256 in several core operations. Mining repeatedly hashes a block header to search for a value below the network’s difficulty target, while transaction and block identifiers also rely on SHA-256-based hashing. This makes SHA-256 central to Bitcoin’s proof-of-work design.
The names are easy to confuse. SHA-1 is an older, separate 160-bit algorithm with practical collision weaknesses; SHA-3 is a later family based on a different internal design; and SHA-0 was the withdrawn predecessor to SHA-1. SHA-256 is not a separate family—it is one member of SHA-2.