VMS Help RMS, $WAIT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The Wait service suspends image execution until an asynchronous
    file or record service completes. The same control block that
    is used with the asynchronous file or record service call is
    specified as the parameter for the Wait service. If it is an
    asynchronous file service, the control block is a FAB; if it is
    an asynchronous record service, the control block is a RAB. Upon
    completion of the service, RMS returns control to your program at
    the point following the Wait service call.

                         RAB64 USERS (ALPHA ONLY)

       On Alpha systems, RAB64 can replace the RAB or RAB prefix
       wherever it is used with the Wait service on OpenVMS Alpha
       systems.

    Format

      SYS$WAIT  control-block

  Additional Information (explode) :

• Returns
• Argument
• Condition Values Returned