SHA-256, or Secure Hash Algorithm 256-bit, is a cryptographic hash function used in many Bitcoin processes. It is used to hash blocks in mining (proof of work), create Bitcoin addresses from public keys (with RIPEMD-160), generate transaction IDs (txid) to secure transactions, and construct the Merkle tree for transaction verification.

The SHA-256 algorithm is part of the SHA-2 family published by the National Institute of Standards and Technology (NIST). It generates a 256-bit (32-byte) hash value, making it ideal for securing sensitive data and ensuring data integrity in Bitcoin and other technological applications, such as digital signatures, SSL certificates for secure web browsing, software security, system integrity verification, secure password storage and more.