Characterization of Auction
Auction can differ in the number of participants:
In a supply (or reverse) auction, m sellers offer a good that a buyer requests
In a demand auction, n buyers bid for a good being sold
In a double auction n buyers bid to buy goods from m sellers
Prices are bid (or offered) by buyers and asked by sellers. Auctions may also differ by the procedure for bidding (or asking, as the case may be):
In an open auction participants may repeatedly bid and are aware of each other's previous bids.
In a closed auction buyers and/or sellers submit sealed bids
Auctions may differ as to the price at which the item is sold, whether the first (best) price, the second price, the first unique price or some other. Auctions may set a reservation price which is the least/maximum acceptable price for which a good may be sold/bought.
Without modification, auction generally refers to an open, demand auction, with or without a reservation price (or reserve), with the item sold to the highest bidder.