CPA stands for cost per action. It is a payment per conversion that an advertiser pays when a visitor takes an action on their site, such as making a purchase in their shop. It is a method of online marketing where the advertiser only pays the publisher for how many customers take a particular action, such as making a purchase. This type of advertising can be very profitable for the advertiser as they only pay for leads that bring them profit and not for those that do not. This forces affiliates to send only relevant traffic to e-shops.