In philosophy, "identity and individuation" is an interesting topic. Saul Kripke, a logician, wrote a book titled that. Philosphy of logic has solved some puzzles there.

Identity: what makes us humans? Individuation: What makes human X different from human Y

We can further go down the abstraction: Identity: what makes me 'me'? Individuation: what makes me at X (time, space) different from me at Y (another time, another space).

Whenever we speak of spatio temporal career of an object (object in general, not from programming), there we see the issue of identity.