Ethereum Classic is a digital currency created as a result of the hard fork of the Ethereum blockchain in July 2016. The compromise of an organization known as the DAO (which had made use of Ethereum's smart contract features) led to the Ethereum Foundation deciding to implement a hard fork. This hard fork rolled back all DAO-related transactions and allowed the original smart contract contributors to withdraw their funds.
The new blockchain created by the hard fork inherited the name Ethereum, and continued to be maintained by the Ethereum Foundation development team. The remaining portion of the community continued to run the original Ethereum blockchain, which became known as "Ethereum Classic."