SHA-256 is a cryptographic hash function that produces a fixed-size 256-bit (32-byte) hash value from any input data. It is widely used in various security applications and protocols, including Bitcoin and other cryptocurrencies, to ensure data integrity and authenticity. The output, known as a hash, is unique to the input data, meaning even a small change in the input will result in a completely different hash. This function is part of the SHA-2 family, developed by the National Security Agency (NSA) in the United States. SHA-256 is considered secure and is resistant to attacks, making it a popular choice for securing sensitive information and verifying digital signatures.