Google Adsense

AdSense delivers relevant text and image ads that are precisely targeted to your site and your site content. And when you add a Google search box to your site, AdSense delivers relevant text ads that are targeted to the Google search results pages generated by your visitors’ search request.
You can maximize your revenue potential by displaying Google ads on your website. Google puts relevant CPC (cost-per-click) and CPM (cost per thousand impressions) ads through the same auction, and lets them compete against one another. The auction takes place instantaneously, and, when it’s over, AdSense automatically displays the text or image ad(s) that will generate the maximum revenue for a page -- and the maximum revenue for you. Sources of this articel Google Adsense