Web3 is a collection of libraries that allow developers to interact with a decentralized application (DApp) on the Ethereum blockchain. It enables developers to write and deploy smart contracts, create wallets, and send transactions to the Ethereum network. Web3 provides an API for interacting with the Ethereum blockchain, allowing developers to access data stored on the blockchain and build applications on top of it. Web3 also provides tools for developers to create their own decentralized applications (DApps).