Cost Per Engagement (CPE) is the online advertising pricing structure. CPE model means advertising impressions are free, advertiser pay only when a user engages with in the ad unit. Engagement is defined in any number of ways, including when a user rolls over an ad unit expanding a full-page overlay, playing a game, taking a poll, or taking a product tour.
CPE model will charge advertisers only when a user interacts with their ads. For example these units will appear like standard display ads with a few seconds of preview video, where users mouse over the CPE ads to display a Flash window that will show the full clip without leaving the page.
CPE approach has given advertisers a choice between quantity and quality, ad formats can be of video, rich media, etc,.