The Aether is the lifeforce of the planet. It exists within and around everything in Amaranthine, and all the other worlds that exist in the Amaranthine universe. Strictly speaking, without the Aether, the world would simply shrivel and die.
The Aether can be manipulated by individuals known as Mages, and through this manipulation many extraordinary feats can be achieved. The Council of the Aether are responsible for upholding the many laws regarding this Aether manipulation, along with the overall running of Amaranthine on a day-to-day basis.