Ethereum Classic is an open-source, blockchain-based computer platform with smart contract (scripting) functionality. Ethereum Classic is not a new cryptocurrency, instead it is a split of an existing cryptocurrency, Ethereum.
Both blockchains are identical in all respects up to and including block 1920000, where the hard-fork was implemented as a refund of the DAO tokenholders, this means that all transactions carried out on the Ethereum blockchain until this hard-fork are valid on the Ethereum Classic blockchain.
Ethereum Classic offers the same functionality as Ethereum, such as creating and implementing smart contracts and decentralized apps. It also has the same specifications, such as average block time, size and reward.
How did Ethereum Classic (ETC) arise?
Ethereum Classic appeared as a result of a disagreement with the Ethereum Foundation about the DAO Hard Fork. It united the part of the Ethereum community that disapproved of the hard fork on philosophical grounds. Users who had ETH before the DAO hard-fork (1900000th block) received the same amount of ETC after the fork.