Source : Free On-Line Dictionary of Computing

wall clock time
     
         The elapsed time between when a {process} starts to
        run and when it is finished.  This is usually longer than the
        {processor time} consumed by the process because the {CPU} is
        doing other things besides running the {process} such as
        running other user and {operating system} processes or waiting
        for disk or {network} {I/O}.
     
        (1998-03-13)