Something verboten is forbidden. It isn't allowed or permitted.
If this word looks and sounds odd, that's because it comes straight to English from German. The concept is simple: anything verboten is forbidden to do or say. Lying in court is verboten. Wearing a hat in church is verboten. Many swear words are verboten to say on TV (or at the dinner table). A verboten act could be illegal or just something frowned upon, like a taboo. Different cultures believe different things are verboten.