Bid

Bid is the price at which a buyer is willing to purchase an asset. In an order book, bid generally refers to the buy side of the market.

Best bid is the highest available price among active buy orders. For example, if buyers are bidding $59,900, $59,950, and $60,000, the best bid is $60,000.

Bid and ask

The opposite side consists of ask orders from sellers. The difference between the best bid and best ask is the spread.

A trader using a market order to sell will generally execute against available bid orders. A trader using a market order to buy will generally execute against available ask orders.