A Second-Price Sealed-Bid Auction is a type of auction where bidders submit their bids without knowing the others' offers. Each bidder writes down their maximum willingness to pay for an item, and these bids are kept confidential until the auction ends. The winner is the bidder who offers the highest amount, but they only pay the second-highest bid. This format encourages bidders to bid their true value, as they won't pay more than necessary, making it a fair and strategic way to determine the item's price.