Learner's definition of ENERGY
1 : ability to be active : the physical or mental strength that allows you to do things
The kids are always so full of energy.
They devoted all their energy to the completion of the project.
I have a lot of nervous energy. [=energy that comes from being nervous]
2 [noncount] : natural enthusiasm and effort 3 [noncount] : usable power that comes from heat, electricity, etc. 4 technical : the ability of something (such as heat, light, or running water) to be active or do work
5 [noncount], informal : a type of power that some people believe a person or place produces