Question: What is energy?
Energy is a measure of an object's capacity to do work.
Doing work means making an object move differently (speed up or down or change direction) or causing any kind of change to happen (chemical or physical change or any other you can imagine).
So the more energy something has, the more it can do or cause to happen.
At KS3 you learned there were 9 types of energy.
But actually these are all just specific names for only two real types of energy and it is better to start thinking of Energy as existing in only the two forms; these are Kinetic Energy and Potential Energy.
Kinetic Energy is movement energy; ie movement about the room, or movement of the particles at the atomic level that cannot be seen.
Potential Energy is energy that is stored invisibly in the object. It might help to think of it as stored movement, such as when you fall on a trampoline.
The total energy of every object exists as a mixture of these two forms.
Total Energy = Kinetic Energy + Potential Energy