- 
        window gravity 
      
- 
        When windows are resized, subwindows can be repositioned automatically
        relative to some position in the window. This attraction of a
        subwindow to some part of its parent is known as window
        gravity. 
      
- 
        window manager 
      
- 
        Manipulation of windows on the screen, and much of the user interface
        (policy) is typically provided by a window manager client. 
      
- 
        window manager shell 
      
- 
        A subclass of shell called wm-shell that interacts with
        the window manager.