SHA-2 is a family of cryptographic hash functions designed by NSA and published in 2001. It includes several variants, such as SHA-224, SHA-256, SHA-384, and SHA-512, which differ mainly in output size. These functions take an input and produce a fixed-size string of characters, which appears random. SHA-2 is widely used in various security applications, including digital signatures, certificate generation, and data integrity verification. It is considered more secure than its predecessor, SHA-1, as it is less vulnerable to collision attacks, where two different inputs produce the same hash output.