Bid

A bid is an offer to buy an asset at a specific price, resting on the buy side of an exchange's order book. The highest bid at any moment is called the best bid, and it represents the most a buyer is currently willing to pay. When you sell with a market order, you are selling into the bids.

For example, if the best bid on ETH/USD is $3,000 for 5 ETH, a trader who market-sells 2 ETH receives $3,000 per coin from that bidder, and the bid shrinks to 3 ETH. If someone sells more than 5 ETH at market, the remainder fills at the next bid down, at a slightly lower price.

Bids matter because they define the price you can actually sell at right now, which is always a little below the price you could buy at. The gap between the best bid and the best ask is the spread, and dense bids near the current price generally mean it is easier to sell size without pushing the price down.