Raydium is an automated market maker (AMM) platform built on Solana, where users can swap, trade, and provide liquidity to earn yield on digital assets. However, unlike other AMM platforms, Raydium's AMM provides on-chain liquidity to Serum's central limit order book. This means that Raydium's users and liquidity pools have access to the order flow and liquidity of the entire Serum ecosystem, and vice versa.