A list (record) of outstanding or resting limit orders that is maintained by a specialist at an exchange/ trading venue, and is used to show the interest of buyers and sellers in a specific security. A limit order book shows such orders to buy or sell a security at a specific price or better. Limit order books (LOBs) match buyers and sellers financial markets, nation-wide and worldwide, determining which orders can be fully or partially executed at the prices specified or better levels.

The lowest price for which there is an outstanding limit sell order is the best ask price and the highest limit buy price is the best bid price. Limit orders are collected and listed in the LOB, which contains the amounts and the prices at different levels for all limit buy and sell orders.