Hallucination are not illusions see note below. Hallucination can be auditory, olfactory, visual, or tactile. Hallucinations are false perceptions or unreal apparition. They do not correspond to the stimuli that is present and have no basis in reality. You have to remember that what is an hallucination in one culture, is not in another.

NOTE: Illusions correspond to the stimuli present and may be only a trick of the eye.