Source : Free On-Line Dictionary of Computing

Windows Messaging
     
         {Microsoft}'s {Internet} {electronic mail}
        application, formerly called {Microsoft Exchange}.
     
        (1998-07-05)

windows messaging
     
         An {inter-process communication} facility usually
        provided by vendors of {graphical user interfaces} for
        {concurrent} {operating systems}, such as {Microsoft}, The {X
        Consortium} and {Apple}.
     
        The system software translates hardware {interrupts} from
        various input devices into messages according to the current
        input context (e.g. the active {window} of the frontmost
        {application}).  Each message is a short piece of information.
        A message's format depends on its type, which is usually
        encoded in its first field.  The message is sent to the
        {client} application using some communication {protocol}
        (e.g. {shared memory}, internal {socket}, network socket).
        The client application dispatches the message and performs any
        actions required.  The messages can also be sent by client
        applications.  This provides convenient and flexible
        inter-process communication.
     
        (1998-07-06)