Energy can mean various things:

• In physics, energy is a property of matter and space. It can be transferred between objects. It can be converted in its form. It cannot be created or destroyed.
• In economics it may mean the ‘energy industry’, as in fuel or electric power distribution.
• Energy can be used to heat, move or illuminate.
• In everyday use, the word is used to describe someone acting or speaking in a lively and vigorous way.