I think you are referring to the works cited in the bibliography, i.e. the works that are referenced in the citations. If we know who produced a work, e.g.its author, we say it is attributed to them; if we don't know, it is unattributed. Note that this isn't quite the same as 'anonymous'. For example a work can be attributed to an institution, e.g. UNESCO, without our knowing who wrote it. The Dead Sea Scrolls, on the other hand, are unattributed.