Definition of pop-under in English:

pop-under

Syllabification: pop-un·der

adjective

Computing
Relating to, or denoting an additional window, usually an advertisement, that is under a web browser’s main or current window and appears when a user tries to exit.
More example sentences
  • The latest pop-window trend to hit the Internet is the pop-under window.
  • Pop-up ads and their newer incarnation, the pop-under ad, are often not appreciated by users on the Web.
  • In terms of display ads, the banner has been supplanted to a certain extent by pop-over and then pop-under ads with the idea that bigger is better and maybe the element of surprise will help.

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