An auction in which there is no set starting price, and whoever bids the highest wins, regardless of how little that bid might be.
The bidding is started at $0, and any bid above that can win. There is no minimum bid. There are no set bidding increments. This is done when the seller wants to get rid of everything -- even if they can't get a good price for it. In theory, the seller is forbidden to bid directly or indirectly on the lots.
Most auctions are not absolute auctions.