Nonexistent things

A hallucination is a perception in the absence of an external context stimulus that has the compelling sense of reality. They are distinguishable from several related phenomena, such as dreaming (REM sleep), which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpre

year that does not exist in the Anno Domini / Common Era year-numbering system

phenomenon where a friendship or other interpersonal relationship takes place in imagination

color that cannot be perceived under ordinary viewing conditions

concept in metaphysics