"According to the first line of the screen man page, "Screen is a full-screen window manager that multiplexes a physical terminal between several processes (typically interactive shells)." That's a mouthful. It's also a little misleading.
"When I think of a window manager, I think of an application that manages GUI windows on a desktop. When the screen documentation refers to a "window," it means a virtual terminal that is running some application. By "window manager," it means that screen manages one or more virtual terminals. By "full-screen," it means that screen can expand to the limits of the real terminal that contains the screen session. And by "multiplexes," it means that screen can control a number of virtual terminals and switch the view to any one of them and not interrupt the running of any of the others.
"While that is the gist of what screen does, that's not the whole picture. When you execute the screen utility, you are really spawning a management process and connected to it. This management process is also known as a screen "session." You can disconnect from the process at any time and leave everything running just as if it were running in a terminal. You can also create a number of different virtual terminals, each running its own application, and switch among them. When you create these virtual terminals, you can almost think of them as part of a tabbed terminal emulator such as Terminal.app on Mac, gnome-terminal on Gnome, or konsole on KDE, except without the visible tabs."
