A belief of another dimensional world outside or embedded in this one.
Some people believe you should access it others believe to stay out if it. Most people do not believe in it.
Person 1 : There is no spirit world.
Person 2 : How do you know? Maybe you just can't see it with your five senses.
Person 1 : Your acting crazy, go see a psychiatrist.
Person 2 : Quantum Physics suggests that I am not.