Have you ever connected to a new website and had uninvited new windows open on your computer screen? This uninvited window is a Pop-Up and may present some type of unsolicited product advertising. One inconsistency with the Pop-Up window is that there are many sites that produce Pop-Up windows offering information that is a vital and necessary part of a particular site.
Although there are many variants on the Pop-Up window theme, most of them contain no menu bar and force you to select an item from a menu before they will close as there is no Close Window gadget to allow you to get rid of the Pop-Up window.