Full Idea
The modern concept of a kind essence is a set of intrinsic properties that are individually necessary and jointly sufficient for the membership of something in a class of things, or 'kind'.
Gist of Idea
A kind essence is the necessary and sufficient properties for membership of a class
Source
Anjan Chakravarrty (Inessential Aristotle: Powers without Essences [2012], 2)
A Reaction
I am always struck by the problem that the kind itself is constructed from the individuals, so circularity always seems to loom.