A measure of the liquidity of a particular market or sector at a given point in time or during a period of time. Depth of market (DOM), also order book, is a window or chart display that enlists all open buy and sell orders available on an exchange at different price levels for individual securities (or broadly any types of tradable assets). In this sense, it reflects the supply and demand for tradeable securities in an active market. Such securities include stocks, futures contracts, etc. Specifically, the list shows the number of open buy and sell orders for a given security.

The more orders on both sides, the deeper or more liquid, the market is perceived be, and vice versa.

It is also known as market depth.