Quintessence

Quintessence - often shortened to QS - comes in two variations. It's a form of energy, its source being the Nether, as well as a sort of material that fills the universe.
In mostly western continents, this phenomenon is called magic. Unexplainable and powerful. QS is merely the scientific side of the same thing.

Manifestation

Realstically speaking, QS is invisible to the naked eye. It gets depicted in different ways according to its corresponding cultures - some describe it as colorful, flying orbs, while others say it's like a dark cloud that wraps over the world, and so on. In a way, none of those are incorrect, since this energy is rather flexible and dynamic.
Greylocks are the only ones who are naturally capable of seeing the way it manifests in.
All non-human beings are made of QS, thus the name quintessence beings. It's also the reason behind how every person's abilities are different; since they are made of this ever-changing energy and every creation differs from another, it comes off as "customized" weapons, healing pace, and so on.

Localization

The Nether itself is made of QS too. Due to its density, it tracks other forms of energy and triggers characteristics similar to dark energy, thus making it capable of expanding that realm as well as creating the real realm.

Type

Metaphysical, Astral