Which characteristic defines a reserve auction?

In a reserve auction, the defining characteristic is that the seller sets a minimum price, known as the reserve price, that must be met for the sale to occur. If bidding does not reach this minimum, the seller is not obligated to sell the item. This allows the seller to maintain some control over the sale price and helps ensure they do not settle for an amount that is lower than their expectations.

In contrast, other auction types or characteristics could include conditions where bids are irrevocable or where a down payment is required to participate, but these are not defining traits of a reserve auction. Likewise, in this auction format, it is not guaranteed that the highest bidder will win if their bid does not meet the seller's minimum price. The reserve price serves as a protective measure for the seller, distinguishing it from auctions where the highest bid wins without conditions.