What is Authentics?

Legal Definition
Civ. law. This is the name given to a collection of the Novels of Justinian, made by an anonymous author. It is called authentic on account of its authority.

2. There is also another collection which bears the name of authentics. It is composed of extracts made from the Novels, by a lawyer named Irnier, and which he inserted in the code at such places as they refer; these extracts have the reputation of not being correct. Merlin, Repertoire, mot Authentique.
-- Bouviers Law Dictionary
Legal Definition
In the civil law. A Latin translation of the Novels of Justinian by an anonymous author; so called because the Novels were translated entire, in order to distinguish it from the epitome made by Julian. There is another collection so called, compiled by Imier, of incorrect extracts from the Novels and inserted by him in the Co.de, in the places to which they refer.
-- Black's Law Dictionary
Legal Definition
A collection of the novels of Justinian.
-- Ballentine's Law Dictionary