Full Idea
An 'individual essence' is a property that in addition to being essential is also unique to the object, in the sense that it is not possible that something distinct from that object possesses that property.
Gist of Idea
An 'individual essence' is possessed uniquely by a particular object
Source
Adolph Rami (Essential vs Accidental Properties [2008], §5)
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.10
A Reaction
She cites a 'haecceity' (or mere bare identity) as a trivial example of an individual essence.