Series of images, thoughts, and emotions, often with a story-like quality, generated by mental activity during sleep; the state in which this occurs
A dream is a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep. Humans spend about two hours dreaming per night, and each dream lasts around 5 to 20 minutes, although the dreamer may perceive the dream as being much longer than this. Wikipedia