energy

Energy is the capacity for activity or the exertion of power. (noun)

An example of energy is a person being able to run five miles just after waking up.
An example of energy is what is created by a wind turbine.

See energy in Webster's New World College Dictionary

noun pl. energies

force of expression or utterance
1. potential forces; inherent power; capacity for vigorous action
2. such forces or power, esp. in action: to apply all one's energies
strength or power efficiently exerted
1. those resources, as petroleum, coal, gas, wind, nuclear fuel, and sunlight, from which energy in the form of electricity, heat, etc. can be produced
2. the available supply of such usable resources: an energy shortage
Physics the capacity for doing work: abbrev. E

See energy in American Heritage Dictionary 4

(ĕnˈər-jē)

noun pl. en·er·gies

The capacity for work or vigorous activity; vigor; power. See Synonyms at strength.
a. Exertion of vigor or power: a project requiring a great deal of time and energy.
b. Vitality and intensity of expression: a speech delivered with energy and emotion.
a. Usable heat or power: Each year Americans consume a high percentage of the world's energy.
b. A source of usable power, such as petroleum or coal.
Physics The capacity of a physical system to do work.