CPACost per Action occurs when the advertiser only pays when an agreed action has been performed, such as making a purchase or requesting more information.
CPCCost per Click - The price paid by an advertiser for a single click on its ad that brings the end users to their intended destination.
CPECost-per-Engagement - CPE model means advertising impressions are free - advertiser pays only when a user engages within the ad unit.
CPICost Per Install - The publisher's charge to the advertiser each time a download is completed on a user's device.