Definition: Pricing based on the number of sales transactions your ad generates. Since users may visit your site several times before making a purchase, you can use cookies to track their visits from your landing page to the actual online sale. Also known as cost-per-acquisition or pay-per-sale
FirstClickSEO Commentary: A relatively new tracking method–paying out only when an actual sale takes place. Similar to Cost per Action, but focused on a sale, not just a lead or different conversion.