ENS (Ethereum Name Service) is a decentralised naming system built on the Ethereum blockchain. It allows users to register human-readable domain names, called ENS domains, and link them to specific Ethereum addresses or content. With ENS, users can send and receive cryptocurrency to a simple, easy-to-remember name rather than a long and complex address. ENS also supports features such as subdomains, reverse resolution, and integration with other decentralized applications on the Ethereum network.