1. appear or arrive unexpectedly or for a short time
problems keep popping up, pop up for a chat, pop-up ad/blocker/shop
As a phrasal verb, 'pop-up' means to appear or occur suddenly usually for a short time. As an adjective or noun 'pop-up' can describe a book or greeting card which contains three-dimensional pictures made from paper that are revealed when the page is turned. A pop-up screen or menu is a window that opens on your computer or phone that can be closed quickly. Pop up stores or restaurants are businesses that open in a temporary location for a short time.