Uniswap is a decentralized exchange (DEX) built on the Ethereum blockchain that allows users to trade cryptocurrencies directly with one another. It operates using an automated market maker (AMM) model, which means that trades are executed through smart contracts rather than traditional order books. This allows for greater liquidity and accessibility, as anyone can provide liquidity by depositing tokens into pools. Users can swap various ERC-20 tokens on Uniswap without needing to create an account or go through a centralized authority. The platform also enables users to earn fees by supplying liquidity, making it an attractive option for both traders and investors in the DeFi space.