CPA (Cost Per Action):
Also known as cost per action or cost per conversion. This metric measures the average amount of money you need to spend in order to acquire one customer. A cost per acquisition pricing model means you will only pay when your ad generates a desired action. The advantage of using this method is that you can choose your definition of an acquisition before the advertising campaign starts. An acquisition can be anything from a sale, to a download, to a registration, it all depends on your objectives. See Cost Per Acquisition.