The Bid Price (also simply called the Bid) is the highest price point (which is below the Ask price) that a prospective buyer is willing to accept in return for their goods.
A Bid price can be either solid or flexible; -solid meaning that the exact number and nothing else will be accepted in return -flexible meaning that the seller is willing to negotiate their price point.
The Bid price is half of the demand side dynamic in price establishment (bid-ask spread)