What does it mean to dream about demons?

A "demon" is an imaginary being, representing a personification of evil. So this dream symbolizes personal invasion and/or control by some evil power. In the dream, the "demon" could represent some authority whose control over one's self is resented; for example, a boss or supervisor. Alternatively, the "demon" could symbolize an addiction or harmful habit over which the dreamer feels no control. The demon is also a very common mechanism for removing guilt from oneself and projecting it onto something else. For example, a man might decide that he is innocent of lustful thoughts by convincing himself that a demon is responsible for that lust.