OnСlick (Popunder) is an advertisement type, which does not block the site screen with annoying banners. Popunders, just like pop-ups, create a separate window with an ad. The difference is that popunder does this in the background without interfering with the main window the user reads. Having finished reading, the user is free to either close the popunder or evaluate the offer and, hopefully, take the desired action. And when used wisely, this format may provide superb results for traffic and conversions.