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. Even a small change in the input will result in a significantly different output, 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, 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.