system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is energy?

What technically is energy, not how it is measured, used, or converted into different forms.  I am looking for what energy actually is.
gpt
Energy is the capacity to do work. Many forms of energy can't be used to do work we would think of as practical (like low temperature differences and low heat), but energy is just that element of physical reality that is the capacity to do work.