A cryptographic hash function used for securing information and messages. Generally, SHA-2 consist of SHA-224, SHA-256, SHA-384, and SHA-512.
The SHA hash functions are five cryptographic hash functions designed by the National Security Agency (NSA) and published by the NIST as a U.S. Federal Information Processing Standard. Hash algorithms compute a fixed-length digital representation (known as a message digest) of an input data sequence (the message) of any length
The five algorithms are denoted as SHA they are: SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512. The latter four variants are sometimes collectively referred to as SHA-2. SHA-1 produces a message digest that is 160 bits long; the number in the other four algorithms' names denote the bit length of the digest they produce.
RFCs and references
Using HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512 with IPsec - RFC 4868
US Secure Hash Algorithms (SHA and HMAC-SHA) - RFC 4634