A type of child-sized window that appears on top of (over or above) the browser display of a visited webpage. This overlay window pane frequently advertises a product or service, but may contain accessibility specifications or important announcements regarding the visited website. The pop-up box covers a portion of the primary display, necessitating a "click through", which intrusion and delay annoys many visitors, and can alienate potential clients or customers. A similar "pop-under" box, which appears in back of (behind or under) the browser window, will only be revealed during the sequential disconnection from the Internet. Blocking software can eliminate pop-ups (and pop-unders), but loading of a webpage can be delayed due to suppression of a necessary dialog box; furthermore, some child windows will not display if pop-up blocking is active. See box, adware, spyware, spam.