DeFi stands for Decentralized Finance, a movement that uses blockchain technology and smart contracts to recreate traditional financial services like lending, borrowing, trading, and saving—without the need for banks or intermediaries. Built mostly on the Ethereum blockchain, DeFi platforms operate through code and are accessible to anyone with a crypto wallet. Projects like Aave, Uniswap, and Compound are key players. DeFi offers users more control and transparency, but also comes with risks like smart contract bugs.