Full Idea
I can understand the notion of real definition as applying to (some) abstact entities, but I have no idea how to apply it to a concrete object such as Socrates or myself.
Gist of Idea
Real definition fits abstracta, but not individual concrete objects like Socrates
Source
Barbara Vetter (Essence and Potentiality [2010], §1)
A Reaction
She is objecting to Kit Fine's account of essence, which is meant to be clearer than the normal account of essences based on necessities. Aristotle implies that definitions get fuzzy when you reach the level of the individual.