Also called Pay Per Action or PPA, Cost Per Action or CPA is a performance-based online advertising pricing model in which the advertiser will only pay if a desired action is fulfilled, unlike Cost Per Click or CPC wherein the advertiser pays for every click on the ad.
The advertiser defines what a valid action for CPA is. It can be a product purchased online, a form submission, or member registration. In this manner, CPA enables advertisers to control their advertising costs.