Originally Posted By: Bill S.
The terms "quantum system" and "quantum states" were yours originally

I wasn't sure, which is why I asked the question.

As I said in my past post, everything in our universe is a quantum system. However, within science we usually reserve that term for where quantum behaviours are discreet (i.e. we see single quantum behaviours, or their effects, rather than a mis-mash of numerous quantum states all at once).

Quantum states are simply when whatever you're measuring has measurable quantums. Keep in mind that quantum = set states with no intermediaries. Electrons can be excited to specific energies in their orbitals, but not energies between those points, etc.