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What is an order book?

A list that is used by exchanges to show the outstanding buy and sell orders for a financial instrument.

Order books are lists used by exchanges to show the outstanding buy and sell orders for a financial instrument. Order books help improve market transparency by providing valuable trading information, such as price and market depth.

Order books on cryptocurrency exchanges have three parts: buy orders, sell orders and trade history.

The buy-side of the order book — often denoted in green — represents all open buy orders below the last traded price. The buy orders indicate trading interest from buyers. The price of the buy order is known as the bid price. For instance, if the buyer places an order to bid for 1.672 BTC at the price of 36,130.9 USDT, then the order will be executed when the bid price is matched by a sell order.

The sell-side of the order book — often denoted in red — represents all open sell orders above the last traded price. The price of an open sell order is known as the ask price. The order will be executed when the ask price is matched by a buy order.

Users may filter all outstanding orders in the order book by price intervals. For instance, they can choose 0.1, 1, 10 or 100 USDT in OKX’s BTC/USDT trading pair.

The trade history of the order book shows the most recently executed orders on the exchange. In each transaction, users can view details, such as price, transaction amount and the timestamp of execution.