In a common-value auction, the bids of other bidders can influence the maximum amount that one is willing to pay for an object, while in a private-value auction this is not the case.

Common-Value Auction

In a common-value auction, all bidders have the same valuation for the auctioned item, but they may have different information about the item's actual value.

Private-Value Auction

An auction in which the value of the item being bid on is subjective and differs for each bidder, based on their private evaluation.