CryptoNote is an application layer protocol that powers several decentralized privacy oriented digital currencies. It aims to be an evolution of the ideas behind Bitcoin. (Cryptonote Whitepaper)
The main difference between the two technologies is that Bitcoin (and most digital currencies) is less opaque than CryptoNote-based currencies due to the latter's blockchain being almost anonymous, contrary to non-Cryptonote blockchains. Unlike Bitcoin, CryptoNote's transactions cannot be followed through the blockchain in a way that reveals who sent or received coins. The approximate amount of a transaction can be known, but the origin, destination, or actual amount cannot be learned!