Exit survey popups or emails are used to reengage the visitors that have decided to leave the website without conversion. They are frequently posted on product pages or checkout pages and pop out if the visitors exit at these points.
The visitors are usually asked what was the specific reason they did not convert (buy, subscribe or similar) and a few other questions that will potentially allow for improvements. To increase likelihood that the visitor will respond, usually some kind of incentive is offered to the responders. Exit surveys are considered to be some of the most useful ways to acquire qualitative data.