0x (ZRX) is a decentralized protocol based on the Ethereum blockchain designed to facilitate trading of ERC-20 tokens. It allows any user or project to create and use decentralized exchanges (DEX), providing the ability to trade tokens without having to rely on centralized exchanges. The 0x protocol uses smart contracts to ensure security and transparency of transactions, and the ZRX token is used to govern the protocol and pay transaction fees on the network. This makes 0x an important element of the DeFi (decentralized finance) ecosystem, promoting greater adoption and use of decentralized applications and exchanges.