Something that has no material form or physical substance can be described as incorporeal. If you believe in spirits or ghosts that can't be touched or seen but only felt, then you believe in the incorporeal.
Incorporeal comes from a combination of the Latin root words in- meaning "not" and corpus meaning "body." Combined they form incorporeus, meaning "without body," which is precisely what something incorporeal is. A haunted house is plagued by incorporeal, or immaterial spirits. You don't see them, but they are there, rattling windows, slamming doors, scaring the living daylights out of you.