Aether is... energy. It makes up the base of all living beings and many of the objects in the world. There's much more to it than that, but that's a very basic idea. It can be manipulated and aspected - there are different elements - and can be used to do magick or to assist in healing the body and mind.

[ He smiles. ]

Whole books have been written on it and its uses, in all honesty.