Energy

^{The definition of energy is the ability to do work or to make something move or change in some way. ... However, it can be described in many different categories: form of energy (heat, light, motion, electrical, chemical, nuclear, and gravity); potential or kinetic energy; renewable or non-renewable.}

To explain energy, you can start with the analogy that food and sleep are what give our bodies the energy we need in order to be active through the day. Your human energy is what gives you the ability to jump, run, play, yell, or do anything else that involves moving your body, or even using your brain. Because we can measure that energy, we know how much it takes to do most of the things we do with our bodies, like running, doing jumping jacks, or riding a bike.