Arcaniferous Æther

Æther is everywhere. It pervades every corner of the world. Every stone, every leaf, every breath of air, every drop of water, every gout of flame.
It grows rich with possibility. It stagnates and turns foul. It bursts into spontaneous motion.
There is no single being incapable of affecting the æther, for the æther affects every being. There are only those who do not have the patience.

- Address of the Grand Arcanist to Prospects at the Crown Academy of the Arcane

The æther is the universal medium through which magical energy (mana) is manipulated. It is perhaps the most actively researched topic among scholars of all fields.
Manipulation (commonly, spellcasting) is the directed effort of an individual to manipulate æther, drawing forth, shaping, and directing mana.
Manifestation is the term describing that release of mana. A manifestation might last for but a moment, or in perpetuity until some other manipulation causes it to break down.

Manifestation

Æther is rarely visible itself, being tricky to discern from the manifestations created by manipulating it.
Quiescent æther is not perceivable by the common sapient beings, although a manipulation of the first order allows one to see, or otherwise detect, the presence of magic by how it perturbs æther.
Active æther - that which is conducting mana - gives off numerous sensory effects. These include a visible glow (arcanoluminescence),  smell or taste (æthichor), and a sensory effect parallel to vibrations but with no physical movement (æther libration). Sensitivity to the latter is more strongly dependent on an individual's ancestry.
The minutae of these sensory effects seems to vary on myriad variables, but perhaps most prominently the nature of the individual and the manipulation deployed.

Localization

Though æther permeates all, it is far from uniform, and consequently difficult to describe with theory. However, two of the most common variations observed of æther are the naturally occuring zones of high and low magic.
High magic regions often cause manipulations to release more energy than intended. In rare cases they can manifest what is commonly called "wild magic", where manifestations occur without a manipulation.
Low magic regions

Type

Metaphysical, Arcane