There are several other operations that can obscure windows or hide them completely. First is the idea of ``iconization''. Depending on the window manager, this can be done in many different ways. In twm, many people configure an icon manager . This is a special window that contains a list of all the other windows on the screen. If you click on a name (depending on the setup, it could be with any of the buttons!) the window disappears--it is iconified. The window is still active, but you can't see it. Another click in the icon manager restores the window to the screen.
This is quite useful. For instance, you could have remote xterms to many different computers that you occansionally use. However, since you rarely use all of them at a given time, you can keep most of the xterm windows iconified while you work with a small subset. The only problem with this is it becomes easy to ``lose'' windows. It is also easy to create new windows that duplicate the functionality of iconified windows, since you forgot about the iconified windows.
Other window managers might create actual icons across the bottom of the screen, or might just leave icons littering across the root window.root window
Another operation most window managers support is maximization. In twm, for instance, you can maximize the height, the width, or both dimensions of a window. This is called ``zooming'' in twm's language although I prefer maximization since different applications respond differently to changes in their window size. (For instance, xterm won't make the font bigger, it will give you a larger workspace!)
Unfortunately, it is extremely non-standard on how to maximize windows.