An exit popup is a commonly used form of popup message that attempts to keep users on your website when they attempt to abandon it. It appears when visitors move their mouse up to their navigation bar to leave your site, and the popup explains why they should stay or download your offer.
Exit popups are used to make sure the user intends to leave a site or to induce them to stay. If the site in question is an e-commerce retailer there is a likelihood that a special offer will be made for a discount if an order is made. If an order is in the process of being made when the exit is effected, the popup might offer a special price for the purchase to induce the user to continue.