For the scientific concept of energy, please see Energy.

Energy is a term used by humans to describe intangible, but perceptible, variations in emotional and physical stamina and motivation. While "low energy" can result from low caloric intake, "energy" in this sense is not connected to the physical quantity of energy. In fact, many caffeinated "energy drinks" contain no caloric content. Extreme low energy is known as fatigue.

Energy and mood disorders

Often, the hypomanic and subdepressive stages experienced by cyclothymic persons are described as variations in energy: the hypomanic or manic person exhibits (along with other symptoms) extreme elevations of energy, while the depressive person exhibits low energy levels.

Concepts of energy

Various concepts of energy exist. In Western usage, "energy" normally refers to motivational energy and ambition; to describe someone as "energetic" means he or she is highly motivated and very active. "Energy" is also sometimes used to describe crowd phenomena (e.g. "at the rock concert, the energy was incredible") to indicate an alert, active, and (in some cases) potentially dangerous group of people.

Spiritual energies, such as qi and kundalini, are often described in Eastern spiritualities, many of which focus on harnessing positive, or desired, energies, and expelling negative energies.

Distinct types of energy are purported to exist. For example, a person going through a divorce may be in excellent physical health, but describe himself as having "depleted emotional energy." Artistically inclined persons often speak of a "creative energy".

Manipulating energies

No specific physical manifestation of motivational "energy" has been discovered, but people in many cultures are aware of these "energies" and, often, try to harness them. For example, the stimulant caffeine is heavily used in Western societies for the "energy" it supposedly provides, though it has no nutritional value. Many Americans believe they are not energetic enough, and consume foods and dietary supplements believed to enhance energy levels.