A hallucination is a visual, auditory, or some other type of sensory distortion that is mistaken for something real. These can be brought on by a variety of different factors, such as being under the influence of drugs.

In The Remnant, Mac McCullum experiences what others thought was a hallucination, or a "cowboy marriage" as stated by Abdullah Smith -- that one of God's angels met him by a river turned to blood near a dam to show him that believers could still get clean drinking water from the bloody rivers and springs brought about by the third Bowl Judgment.