PPC is an acronym for pay per click. Pay per click is an online advertising model in which advertisers display ads on various websites or search engines and pay when a visitor clicks through. Bid-based PPC involves an auction in which advertisers compete with other advertisers by setting the max bid -- or highest amount they're willing to pay -- for each click. Each time a visitor triggers the ad spot, the auction process pans out to select which ad will be displayed.