energy

(noun): The impetus behind all motion and all activity.
(noun): The capacity to do work.
(noun): A quantity that denotes the ability to do work and is measured in a unit dimensioned in mass × distance²/time² (ML²/T²) or the equivalent.
(noun): An intangible, modifiable force (often characterized as either 'positive' or 'negative') believed in some New Age religions to emanate from a person, place or thing and which is (or can be) preserved and transferred in human interactions; shared mood or group habit; a vibe, a feeling, an impression. (Compare aura.)
(noun): (often plural) The external actions and influences resulting from an entity’s internal nature (ousia) and by which it is made manifest, as opposed to that internal nature itself; the aspect of an entity that can affect the wider world and be apprehended by other beings.
(noun): A measure of how many actions a player or unit can take; in the fantasy genre often called magic points or mana.