Yes, it means a particular kind of new window. It's often small. It appears on top of what you're trying to read. It interrupts you. It usually to get you to do something. It may be hard to figure out how to close it. It's called a "Pop-up" because it appears suddenly. (To "pop up" can mean to "appear suddenly or surprisingly.") Often it appears without your clicking anything. Because they are usually annoying ads, many web browsers have a setting to "block pop-ups."