VMS Help SCA, SCA Topics, Glossary, library_number  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Refers to the position of a single physical library in a library
    list. This can be used with any command that refers to a library
    already in the library list. For example, the command SET
    NOLIBRARY 1 removes the first library from the library list, and
    the command LOAD/LIBRARY=2 FOO.ANA loads the file FOO.ANA into the
    second library on the library list.