What is the meaning of Ethereal?

Pertaining to the presupposition of an invisible air-like element permeating all of space, or to the higher regions beyond the earth or beyond the atmosphere.

Pertaining to the immaterial realm, as symbolically represented by, or (in earlier epochs) conflated with, such atmospheric and extra-atmospheric concepts.

Consisting of ether; hence, exceedingly light or airy; tenuous; spiritlike; characterized by extreme delicacy, as form, manner, thought, etc.

Ellipsis of ethereal wave (“music genre”).

Source: wiktionary.org