0x Protocol is an open-source protocol used for building decentralized exchanges (DEXs) on the Ethereum blockchain. It enables the peer-to-peer exchange of ERC-20 tokens without the need for a central authority or custodian. Through 0x Protocol, users can trade on multiple DEXs without having to manage multiple accounts or deposits. It also allows for the creation of new trading applications that can tap into the liquidity of all connected DEXs, creating a larger and more diverse marketplace.