Energy/ˈenərdʒi/ Definition 1 of 3Pro Tip 1/3Physical Exertion Used to describe someone's stamina or strength during physical activities. After the marathon, he had no energy left. Pro Tip 2/3Activity Level Reference to how active or lively a person or environment feels. The festival was full of energy. Pro Tip 3/3Mental Sharpness Talks about the ability to think or concentrate, not just physical activity. I need more energy to focus on this exam.