An auction is a way of buying and selling things (goods). In a shop, the price of a thing is fixed and you have to pay that amount. In an auction, you tell the seller how much money you want to pay for the thing.How much you want to pay is called a ‘bid’ or an ‘offer’. The person who makes the biggest offer will be the person who buys the thing. There might be a minimum price called a ‘reserve’. If the biggest offer is smaller than the reserve, the seller does not have to sell the thing.