It is Cost per Engagement.
A new measure of performance in online advertising. After CPM, CPC and CPA we have this CPE which has no relation with impression but only with the engagement i.e when any user engages with the brand content.
This measure actually differentiates between quantity and quality.
Engagement can be defined as a user interacting with an ad in any number of ways, including viewing, sharing, voting, commenting, reviewing, playing a game , etc.
CPE campaigns are mainly video campaigns as it initiates used to engage with the creative.