ˈpop-under BrE AmE noun [countable]
a ↑ window containing an advertisement, that suddenly appears under another window on a computer screen when you are looking at a website ⇨ pop-up
ˈpop-under BrE AmE noun [countable]
a ↑ window containing an advertisement, that suddenly appears under another window on a computer screen when you are looking at a website ⇨ pop-up
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012