This is something of a hybrid between a raffle and an auction, most commonly organised by fundraisers. Participants buy or win tickets that give them the opportunity to bid on items. A variety of items are for sale and participants can place their bids on any items they wish.
The bids can either all be of an equal fixed amount, or the bidders themselves can specify the individual amounts they are willing to pay for items. When the auction comes to an end, the winning bid is chosen at random. The winning bidder pays whatever amount they bid.