The Secure Hash Algorithm (SHA) is a family of cryptographic hash functions designed to ensure data integrity. It takes an input (or message) and produces a fixed-size string of characters, which appears random. This output, known as a hash, is unique to each unique input, making it useful for verifying data authenticity. SHA is widely used in various security applications and protocols, including digital signatures and password storage. Different versions of SHA, such as SHA-1, SHA-256, and SHA-3, offer varying levels of security and performance, with newer versions providing stronger protection against potential vulnerabilities.