What does SHA-256 mean? 

SHA-256 is derived from the SHA-2 (Secure Hashing Algorithm 2) algorithm which was developed by the U.S. National Security Agency (NSA).

It is a cryptographic algorithm used by cryptocurrencies such as Bitcoin. It is used both in the mining of Bitcoin and in the creation of private keys and public addresses. However, in mining it uses a lot of computing power and processing time, forcing miners to form mining pools to capture gains.