VMS Help DTM, SPAWN, Command Qualifiers, /WAIT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

   /WAIT (D)
   /NOWAIT

   Controls whether the system waits until the subprocess is
   completed before allowing more commands to be issued by the parent
   process. The /NOWAIT qualifier enables you to enter more commands
   while the specified subprocess is running. If you specify the
   /NOWAIT qualifier, you should also specify /OUTPUT to direct
   output to a file (rather than to the screen). This prevents your
   terminal from being used by both processes simultaneously.