Your balance is represented as a cToken when you contribute assets to the Compound protocol, which can be transferred, exchanged, or programmed by developers to build new experiences.
The Compound protocol uses cTokens as a back-end form of currency. If a user sends cryptocurrency to the protocol, cTokens are applied to keep track of the money they've loaned and any interest they've earned. When a user contributes money to the lending pool, they are given a cToken balance in return.