auctorum (abbreviated auct. or auctt.), in zoology is a term used to indicate that a name is used in the sense of a number of subsequent authors and not in its (different) sense as established by the original author. It is often used to refer to a misidentification. auctorum is Latin and means of authors.
The list of synonyms of Tinea trinotella reads Tinea tripunctella (auct. non Denis & Schiffermüller 1775). Although Tinea tripunctella seems to be listed as a synonym of Tinea trinotella, the use of auct. indicates it is in fact a valid species. In this case auct. is used in combination with non, which should be read as: as used in the sense of author(s) but not of the original author. Hence, the concept of the species as used by authors other than the original author was wrong. This wrong concept is a synonym, but not the original species.