system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Is "potential energy" actually energy? Or just a descriptor?

So a boulder on the top of a hill has more potential energy than one at the bottom, right? But isn't that arbitrary? Is it "energized" in the same way it would be by heating it up? 

I suppose what I'm asking is: does "potential energy" actually exist? Or is it just a useful thing to plug into equations?
gpt
>Is "potential energy" actually energy?

Potential energy is only defined relative to a point of reference. 

There is no such thing as "absolute potential energy", which is what you intuitively seem to identify as being "not real". There is a difference in potential energy between a boulder on a hill and a boulder in the valley below. This **difference in potential energy is absolute**. When we say something like a book on a table has potential energy, we implicitly define the ground as a point of reference, relative to which the difference in potential energy is measured. 

>Or just a description?

Of course it's just a description. Like every other form of energy as well. "*Energy*" is nothing tangible. It is simply a number that seems to be (mostly) constant in our universe, if we add up all the forms of energy we know.