Often as aether and more fully as luminiferous aether: a substance once thought to fill all unoccupied space that allowed electromagnetic waves to pass through it and interact with matter, without exerting any resistance to matter or energy; its existence was disproved by the 1887 MichelsonâMorley experiment and the theory of relativity propounded by Albert Einstein (1879â1955).
The atmosphere or space as a medium for broadcasting radio and television signals; also, a notional space through which Internet and other digital communications take place; cyberspace.