Auction of a helmet at Christie's.

Melburne tea auction, print from 1885. Also shows tea being weighed and tasted.

An auction of fresh tuna, in Japan

"Grasmere" on Ferry Road awaiting sale by auction. The auctioneers website says: "A detached Victorian property in need of complete renovation set in open countryside with surrounding grass paddock extending to 8.11 acres. Guide Price: £150,000 - £200,000."

An auction is a method by which 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 their 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, the auction can continue for 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.