Ethereum Classic (ETC) is a platform for building distributed applications (DApps) and smart contracts.
Similar to Bitcoin, Ethereum Classic adopted Proof of Work (PoW) as its consensus mechanism, which builds a consensus as a community. Ethereum Classic is functionally the same as Ethereum, but the issuance cap and reduction periods are different. Specifically, the issuance cap is set at approximately 210 million and the mining rewards are decreased by 20% every 5 million blocks (as of October 2019).
While Bitcoin takes about 10 minutes to mine a block, Ethereum Classic takes about 15 seconds. The smallest unit of ETC is the Wei, which is 0.000000000000000001 ETC.