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.