A hallucination is a perception of something that is not really there. A hallucination can involve any of the senses: hearing, sight, smell, taste, or touch.
The most common hallucinations are seeing (visual) and hearing (auditory) things. For example, the person may hear voices or see an object that other people do not see.
Other types of hallucinations include tasting (gustatory), smelling (olfactory), or feeling (tactile) something that is not there.
Treatment for hallucinations depends on the cause.