The Free On-line Dictionary of Computing (30 December 2018):

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)