An auction is a method of goods or services can be sold and bought. In an auction, the price of an item is not fixed in advance. People wanting to buy the item say how much they are willing to pay for it. This is called "bid". In each round, the bids are evaluated: If certain criteria are met, the auction is stopped and one bidder will buy the item at the specified price. Alternatively there will be another round. If certain conditions are met, the auction will stop, and the item will not be sold. There are different kinds of auctions, with different rules.