Pop-ups are those annoying windows that appear out of nowhere when you visit a website. However, there are many ways to refer to these intrusive elements. One common synonym is "interstitials." These are full-screen pop-ups that often appear between pages or during a transition. Another term used is "overlays," which refers to pop-ups that cover the entire page or a portion of it. "Modal windows" are also a synonym for the pop-ups that require the user to interact with them before they can continue with their browsing session. Lastly, "pop-unders" are pop-up ads that appear behind the current web page and are hidden until the user closes or minimizes the current browser window.