VMS Help RTL Routines, SMG$, SMG$DELETE_VIRTUAL_DISPLAY, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 display-id

    OpenVMS usage:identifier
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Specifies the virtual display to be deleted. The display-id
    argument is the address of an unsigned longword that contains
    the display identifier.

    The display identifier display-id is returned by SMG$CREATE_
    VIRTUAL_DISPLAY.