Cost per click (CPC) is a digital advertising revenue model. Websites use it to bill their advertisers. It is based on the number of visitor clicks on ads that are displayed on the site. An alternative to the CPC model is the cost per thousand (CPM) model. The CPM model is based on the number of ad impressions or views of the ad that is displayed and not clicks. The CPC model is sometimes also referred to as the pay-per-click (PPC) model.