The impetus behind all motion and all activity. / The capacity to do work.

plural of energy

Energy taken from a source that is depleted by extraction (such as fossil fuels).

A source from which useful energy can be extracted or recovered either directly or by means of a conversion or transformation process (e.g. solid fuels, liquid fuels, solar energy, biomass, etc.)

A substance or phenomenon that can be used to produce mechanical work or heat or to operate chemical or physical processes (ISO 13600).

A domestic electricity meter

(chemistry, physics) The energy required to initiate a reaction. For example, the flame from the fuse of a firecracker provides a small initial amount of energy, after which the explosive reaction proceeds by itself, releasing a considerably larger quantity of energy. A small push given to a stable but top-heavy object may cause it to fall over; the potential energy released during the fall was present in the system all along but could not be realized as long as the object was upright and balanced.

(astronomy, astrophysics) A hypothetical form of energy which, it is supposed, is spread uniformly throughout space (and time) and has anti-gravitational properties: it represents a possible mechanism for the cosmological constant, and thus is one of the possible explanations for the current accelerating rate of expansion of the universe; and it is estimated to account for about 74% of the mass-energy of the universe.

(physics) The increase in internal energy of a unit mass of solid when it undergoes sublimation at constant temperature and pressure

Energy that is collected from renewable resources, such as wind, water, or the sun, usually and especially as applied to a category of electrical generation.