Definition
"Aether" (also spelled "ether") historically referred to a hypothetical medium believed to fill the universe and through which light waves traveled. It was thought to be a weightless, transparent substance permeating all space. Think of it as the invisible stuff that carries light, like water carries sound. This concept was later disproven by scientific experiments. Now, it's often used metaphorically to describe the upper regions of the atmosphere or the realm of the abstract. π