A DeFi aggregator is a platform that consolidates various decentralized finance services, such as lending, borrowing, staking, and yield farming, into one interface. It aims to streamline user experience by sourcing the best yields, prices, and liquidity from multiple DeFi protocols. Aggregators help optimize users' returns by automatically finding the most profitable opportunities across various DeFi platforms, reducing transaction costs, and minimizing slippage. They also simplify the complex DeFi ecosystem, making it more accessible to non-technical users.