A delusion is a strongly held false belief that persists despite evidence to the contrary. A delusional individual may believe that she is being spied on or ridiculed, that she has special powers, or that song lyrics contain hidden messages directed specifically at her.
A hallucination is the conscious perception of something (images, sounds, odors, etc.) in the absence of any external stimulus. Examples of hallucinations include hearing voices talking about you, experiencing unpleasant smells, or seeing ghosts.
A delusion an untrue belief; a hallucination is an unreal perception.