(physics) The energy needed to separate the constituent parts of an atom or nucleus; equivalent to the mass defect.

(physics) The energy released by a nuclear reaction; either through nuclear fission or nuclear fusion / Such energy used as a power source.

Energy in the form of electromagnetic radiation emitted from the Sun; especially that part of this energy that is converted into usable thermal or electrical energy by man.

(physics) The sum of the potential energy and kinetic energy of a body or system

(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 underlying background energy of empty space associated with constant vacuum fluctuations.

(physics) Energy stored in a ferromagnetic material as a result of the work done by the rotation of its magnetization

The energy of a system with respect to its centre of gravity

Energy derived from any source other than fossil fuels. / Energy derived from any renewable source, i.e other than fossil fuels or nuclear fission.