Compound is an open-source, autonomous protocol built for developers, to unlock a universe of new financial applications. Interest and borrowing, for the open financial system.
Compound is a transparent, autonomous money market–allowing users & applications to frictionlessly earn interest or borrow Ethereum assets without relying on a counterparty. Compound is the first “liquidity pool” — instead of lending assets directly to another user, you supply liquidity to a market, and users borrow from that market.
The Compound protocol tokenizes balances in the protocol; these are called cTokens. They can be transferred (as an example, to cold storage) or programmed by developers to create new experiences. cTokens accumulates interest through their exchange rate — over time, each cToken becomes convertible into an increasing amount of it's underlying asset, even while the number of cTokens in you wallet stays the same. The current cTokens are listed on etherscan.