With the cost per engagement (CPE) model, advertisers pay for interactions with
adverts, normally placed in videos or applications (such as Facebook applications).
An interaction, referred to as an engagement, usually starts with a rollover (or
mouse-over) that expands the ad. Once expanded, an advert may contain a video,
game, form, or other interactive content. The ad doesn’t take the user away from
the web page, and marketers pay only when an individual completes an action.