Glossary
Order Book
The list of resting buy and sell orders at each price level on a market — the data structure that underlies traditional exchanges and most CEXes.
An order book lists every limit order — buy or sell, with a size and price — that hasn't yet matched. A market order executes against the best resting orders; a limit order sits in the book until it gets matched or canceled.
Centralized exchanges run private order books in-memory; on-chain order books (dYdX v3, Loopring, Serum historically) keep them on the blockchain or post-only-but-on-chain. AMMs replaced the order book with a continuous pricing curve, trading expressiveness for gas efficiency.