Aetherium is the term used typically by scholars that encompasses what mortals term the Feywild, Celestial Planes, and Abyssal Planes. Outside of scholarly treaties it is typically used to refer to all planes of existence outwith Roshar and Death. Those beings native to Aetherium have morals and motives typically alien to mortal thought.
Elemental beings are found primarily in Aetherium, however they are not concentrated in any particular realm.