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

    A list of one or more physical libraries which compose the virtual
    library. The order of the physical libraries is important. A
    module found in one physical library in the library list hides
    the same module in other physical libraries that come later in the
    library list.

    For example, suppose you have three libraries. Library 1 contains
    module A. Library 2 contains modules A, B, and C. Library 3
    contains modules C and D. SCA uses module A from Library 1,
    modules B and C from library 2, and module D from library 3.