Popunder advertising can be a format where an advert opens in a very new browser window or tab behind the person’s active window. It’s designed to be less intrusive than pop-ups, appearing only after the user has left or minimized the primary site window, creating a more seamless browsing experience. https://telegra.ph/Popunder-Advertising-A-Guide-to-Maximizing-Engagement-and-Conversions-11-11