definition of energy 1. beaker of water brought to boil over a hot plate or stove. 2. viscous heat pack (you have all seen them work, you do not have to buy one unless you do not know how they work. 3. popcorn to be popped and eaten (great with your loved one and a movie). 4. battery operated or windup toy car set into motion. 5. children's blocks stacked so that the top block balances precariously. 6. spring-loaded mouse trap (don't get your fingers caught). 7. operating a light bulb 8. walk up and down a flight of stairs a few times (no heart attacks please) 9. turn on a hair dryer.