CPA refers to cost per acquisition. This model means that the advertiser pays
only when an advert delivers an acquisition after the user clicks on the advert.
Definitions of acquisitions vary depending on the site and campaign. It may be a
user filling in a form, downloading a file or buying a product.
CPA is often the best option for advertisers because they pay only when the
advertising has met its goal. For this reason, it is also the worst type for the
publisher, as they are rewarded only if the advertising is successful. The publisher
has to rely on the conversion rate of the advertiser’s website, something that
the publisher cannot control. The CPA model is not commonly used for banner
advertising and is generally associated with affiliate marketing.