Ether is the purest, ethereal form of energy.

Ether governs all movement, motion, energy, heat, sound, etc. In its perfect state it is completely inert (though on Plumamentia it is bound to obey simple and well-defined rules as governed by the Pillars, such as gravity and magnetism) - though Ichor can impose its own will and rules upon Ether (a process which corrupts the Ether and converts it into Mana).