dream : (1) an experience of waking life having the characteristics of a dream (2) a visionary creation of the imagination (3) a state of mind marked by abstraction or release from reality (4) an object seen in a dreamlike state (5) a strongly desired goal or purpose (6) something that fully satisfies a wish — Webster
Dream may refer to a motivating personal ambition or goal, a romantic prospect, or a vision of future change. — Wikipedia
Oneirology is the scientific study of dreams. Current research seeks correlations between dreaming and current knowledge about the functions of the brain, as well as understanding of how the brain works during dreaming as pertains to memory formation and mental disorders. The study of oneirology can be distinguished from dream interpretation in that the aim is to quantitatively study the process of dreams instead of analyzing the meaning behind them. — Wikipedia
The Science Behind Dreaming (Sander van der Linden, Scientific American)
Why Do We Dream? Science Offers a Few Possibilities (Alex Orlando, Discover Magazine)
The Science of Dreams (Rebecca M. C. Spencer, Frontiers for Young Minds)
Here are links to pages about closely related subjects.