system
Given the following post, respond as if you're commenting on Reddit:
human
Where and how is gravitational potential energy stored?
gpt
In general, potential energy is a mutual property of *systems* of objects, not individuals.  There is gravitational potential energy in the Earth-Moon system, but it's not really accurate to say that the energy is stored in either the Earth or the Moon.  Same goes for a thrown baseball, though we often say "the baseball has gravitational potential energy" as a shorthand for "the Earth-baseball system has gravitational potential energy".

One useful perspective is to say that the energy is stored in the gravitational field that occupies the empty space between the two objects.  There's literally nothing there, and yet that empty space "has energy".