Pop-up windows, or pop-ups, are windows that appear automatically without your permission. They vary in size but usually don't cover the whole screen. Some pop-ups open on top of the current window, while others appear underneath.
Blocking pop-ups may interfere with some websites: some websites, including some banking sites, use pop-ups for important features. Blocking all pop-ups disables such features. To allow specific websites to use pop-ups, while blocking all others, you can add specific websites to the list of allowed sites.
Although some browsers blocks most pop-ups, some websites may show pop-ups using uncovered methods, even when blocked.