A first-price auction is a type of auction in which the highest bidder wins the item for sale and pays the amount of their bid. In a first-price auction, bidders do not know the bids of other participants, and each bid is a sealed bid. The highest bid wins the auction and the winner pays the amount of the bid. It is different from the second-price auction ( Vickrey auction) where the winner pays the second highest bid.
Google announced on October 7, 2021 that it will transition to a first-price auction for certain AdSense products such as AdSense for Content, AdSense for Video, and AdSense for Games, which was completed on November 17, 2021, AdSense for Search and AdSense for Shopping will not be affected by this change.