are sensory experiences that occur in the absence of real stimuli
A hallucination is a perception in the absence of external stimulus that has qualities of real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. They are distinguishable from several related phenomena, such as dreaming, 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 imagery, which does not mimic real perception and is under voluntary control. Hallucinations also differ from ``delusional perceptions'', in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional (and typically absurd) significance.
Hallucination