Library /sys$common/syshlp/dbg$help.hlb DEBUG, DEFINE, Qualifiers, /COMMAND  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Specifies that the defined symbol is treated as a new debugger
    command. In this case, parameter is a quoted character string.
    This qualifier provides, in simple cases, essentially the same
    capability as the following DCL command:

    $ symbol := string

    To define complex commands, you might need to use command
    procedures with formal parameters. For more information about
    declaring parameters to command procedures, see the DECLARE
    command.