hal|lu|ci|na|tion «huh LOO suh NAY shuhn», noun.
1. the condition of seeing, hearing, tasting, smelling, or feeling things that exist only in a person's imagination. A person alone in a perfectly quiet room suffers from hallucination if he sees people around him or hears voices. Hallucinations may occur as a result of certain mental illnesses or fever, acute alcoholism, the taking of certain drugs, or other causes.
2. a thing seen, heard, or otherwise sensed when it exists only in a person's imagination.
Useful english dictionary. 2012.