- 
        backing store 
      
- 
        When a server maintains the contents of a window, the off-screen saved
        pixels are known as a backing store. 
      
- 
        before action 
      
- 
        An action of a contact-display that is called when an event is
        dispatched to a contact, but before any other contact input processing
        is performed. 
      
- 
        bit gravity 
      
- 
        When a window is resized, the contents of the window are not
        necessarily discarded. It is possible to request the server to
        relocate the previous contents to some region of the window. This
        attraction of window contents for some location of a window is known
        as bit gravity. 
      
- 
        bitmap 
      
- 
        A pixmap of depth one. 
      
- 
        button grabbing 
      
- 
        Buttons on the pointer can be passively grabbed by a client.
        When the button is pressed, the pointer is then actively grabbed by
        the client. 
      
- 
        byte order 
      
- 
        For image (pixmap/bitmap) data, byte order is defined by the server,
        and clients with different native byte ordering must swap bytes as
        necessary. For all other parts of the protocol, the byte order is
        defined by the client, and the server swaps bytes as necessary.