There are several types of auctions, each with its own rules and bidding processes. The most common type is the English auction, where bidders openly bid against one another, and the highest bidder wins. Another popular type is the Dutch auction, where the auctioneer starts with a high price and gradually lowers it until someone accepts the current price. In contrast, a sealed-bid auction requires bidders to submit their bids privately, with the highest bid winning. Additionally, there are reverse auctions, where sellers compete to offer the lowest price for a product or service. Each auction type serves different purposes and can be used in various markets.