An order book is a ledger that records all orders and trades made in a financial market, such as a stock exchange or cryptocurrency exchange.
The order book displays two main types of orders: bids and asks. Bids are orders to buy a certain asset at a specific price, while asks are orders to sell an asset at a specific price. The highest bid and lowest ask are referred to as the best bid and best ask, respectively.
The order book also displays the size of each order or the number of shares or units of the asset being bought or sold. This information is important for traders as it provides insight into the market sentiment and potential price movements.