What does exit pop up means on a landing page?

First, 'pop-up' - these are the irritating little boxes that demand you respond before it will let you see the page you want to look at.

Next, 'exit pop' up - supposedly less irritating but IMHO really obnoxious because they won't let you leave the page unless you respond - it is really confusing too because you have to decide between 'cancel' and 'stay' - and somehow even cancel does not make it go away.

There is also 'pop under' which is the least obnoxious however spooky because you feel invaded and you are not sure how it got there. This one lets you visit the site without intruding - and even lets you leave. However then you find it under your windows - it is easy to blow it away...

I used to know the exact reason why many traffic exchanges and various applications do not allow pop-ups - and it is something mechanical - it interrupts the process for the system the same way it interrupts what people are doing...

Specifically with a traffic exchange if you are viewing an ad and do not wish to click to respond you can't just stay on there 30 seconds or whatever and then it will automatically rotate to the next ad - however you HAVE TO click the exit pop-up to move forward so that is what interrupts the process.