A smart contract holding reserves of two or more assets that traders swap against, with the price set by a formula over the balances rather than by an order book.
Pools are what let a token trade at all without a market maker sitting on both sides. The depth of the pool decides how much a trade moves the price — thin pools make any real order expensive.
We implement pool integrations against audited protocols rather than writing our own AMM maths, and we show users expected slippage and the worst acceptable price before they sign.