This is the revealing terminology employed by many Etruscologists and some ancient historians to indicate ancient authors, textual or literary sources. The employment of this term exclusively for written sources subconsciously reveals the primacy given to textual information when this is extremely scant and for many topics nonexistent for the Etruscans. Most study of the Etruscans has to be strictly archaeological, based on material culture; once this framework is formed, some opinions of ancient authors (none are Etruscan) can brought into play.
Historical Dictionary of the Etruscans. Simon K. F. Stoddart.