"Utopian" describes a society that's conceived to be perfect. Dystopian is the exact opposite — it describes an imaginary society that is as dehumanizing and as unpleasant as possible.
George Orwell's "Animal Farm," for example, describes a dystopian society in which Napoleon, a pig, represents Joseph Stalin in a farmyard satire on Stalinist Russia and how power corrupts. Other famous dystopian authors include Aldous Huxley, Kurt Vonnegut, and Ray Bradbury. The adjective dystopian describes anything that pertains to or resembles a society such as those described in this sort of literature.