Energy level

This article is about orbital (electron) energy levels. For compounds' energy levels, see chemical potential. A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. The term energy level is most commonly used in reference to the electron configuration in atoms or molecules. In other words, the energy spectrum can be quantized (see continuous spectrum for the more general case).
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Noun
1. a definite stable energy that a physical system can have; used especially of the state of electrons in atoms or molecules; "according to quantum theory only certain energy levels are possible"
(synonym) energy state
(hypernym) energy

the allowable stable states of energy from quantum mechanical principles.

The energy associated with a quantum state .

The path of a given electron's orbit around a nucleus, marked by a constant distance from the nucleus.