(n.) A system that provides you with a multiuse environment on the display device. Separate windows are similar to separate displays on the monitor screen. Each window can run its own application. You open some number of windows for various applications, and the window system handles the communications between each of the applications and the hardware.
Software which allows a computer's video screen be divided into windows which act like a separate input/output devices under the control of different application programs. The user may see the output of several processes at once and choose which one will receive input by selecting its window with a mouse or other pointing device. window manager is the part of a window system which arranges windows on a screen. It is responsible for moving and resizing windows, and other such functions common to many application programs.