Ether

Ether, in common borderland usage, is a term derived from the ancient element of aether (Greek αἰθήρ, aithēr: "upper air"), also spelled æther, originally describing a substance that fills and permeates the regions of the Universe surrounding the planets, and acts as the medium through which electromagnetic waves are propagated. Depending on the theory or field of research in question, it may have several different potential meanings and applications.