A list of buy (bid) and sell orders (offer) for a security or financial instrument that a trading venue (e.g., an exchange) arranges by price level. An order book records (electronically or otherwise) the interest of buyers and sellers (generally, market interest) in a particular security/ financial instrument. The book is used by a matching engine (or manually) to determine which orders can be fully or partially executed.

In markets, liquidity is typically measured through the order book, which constitute the orders placed by traders or their agents to buy and sell securities at different price points.

It is also referred to as depth of market (DOM).