Aether

Aether is a magical essence that flows through everything.
It is invisible to most people, although it can be sensed, and ambient aether can be pulled out of the surrounding area to do magic. 
Aether occasionally will act on its own, without being channeled into a spell. This can create strange natural phenomenon, such as the floating islands. This is rare, however, and usually aether will not cause much disruption without it being controlled by a mage.
It is a force of nature, so it is not inherently good or bad. Aether is very useful in allowing magic, but it is also what creates spirits and monsters. 
As it exists in everything, it forms patterns in the way it flows. These hidden patterns can be deduced and are how the system of glyphs was created. In the stars, the patterns are much easier to observe, as they form the constellations. It is not clear exactly how aether forms patterns in the sky - does aether actually extend up into the celestial sphere, or does it only appear that way? Further confusing the matter is that the constellation patterns are only observable when the stars themselves are. There are also patterns surrounding the sun and moon. 
Aether seems to be connected to the astral plane in some way. The astral plane may be made out of aether, or it may be the source of the magical essence, or both. It is unclear and difficult to get answers, as the astral plane is mysterious and not very well documented.
The origin of aether is also unclear. Some say it simply comes from the astral plane, while others say it was placed there by creator gods, or is a god itself. No matter its origins, the mechanics of aether are largely agreed upon. Various scholars and academies around the world study aether as well as magic, and the basic concept is common knowledge.