Ethereum Classic (ETCUSD) is an Ether fork.
This new cryptocurrency was created in the summer of 2016, after some of the Ether community had not approved the changes suggested by the Ethereum Foundation. Basically, Ethereum Classic is just regular Ether that was in place before the hard fork occurred.
With Ethereum Classic (ETC) being a fork of Ethereum, everyone who had Ether received the same amount of ETC under certain conditions. ETC is a decentralised currency issued by other users who have enough hardware and software resources to support it.
The Ethereum Classic rate depends entirely on supply and demand. Its real value is determined by the total amount of goods and services one can purchase with ETC, as well as by the speculative environment.