1 : ability to be active : the physical or mental strength that allows you to do things [noncount] ▪ 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] [plural] ▪ They devoted all their energies to the completion of the project.
2 [noncount] : natural enthusiasm and effort ▪ She puts a lot of energy into her work.
3 [noncount] : usable power that comes from heat, electricity, etc. ▪ The newer appliances conserve more energy. ▪ an energy crisis ▪ renewable energy —see also nuclear energy
4 technical : the ability of something (such as heat, light, or running water) to be active or do work [noncount] ▪ kinetic energy [plural] ▪ particles with high kinetic energies
5 [noncount] informal : a type of power that some people believe a person or place produces ▪ I sense a lot of negative/bad energy coming from her right now. ▪ There's good/positive energy in this room.