Pay-per-click (PPC)

This term came about in 1998 when the Overture search engine started allowing auction based bidding on placement in their search engine. Also referred to [[ppp]], eventually Yahoo! bought Overture and implemented this advertising system into their search engine now called Yahoo! Search Marketing. Google eventually created a similar program called AdWords in 2001, which is now the dominate provider of pay-per-click advertising.
The difference between pay-per-click and CPM or cost-per-thousand impressions advertising is the advertiser does not pay unless their ad is clicked on no matter how often the ad is shown.