Ethereum uses Keccak256 in a consensus engine called Ethash. Keccak is a family of hash functions that eventually got standardized to SHA-3 (SHA256 is part of a family of hash functions called SHA-2). Ethereum called it Keccak instead of SHA-3 as it has slightly different parameters than the current SHA-3. Colloquially, Ethereum mining is never called Keccak mining because Ethash utilizes mixhashes in a DAG, which is different from Hashcash proof-of-work. Some blockchains utilize Keccak in the same way Bitcoin uses SHA-256, but these are not as common.