Merriam Webster defines a dystopia as "an imaginary place where people lead dehumanized and often fearful lives." Dystopias generally display severe restrictions on what we would consider to be basic human rights, such as the number of children a family can produce, what can be said regarding governmental practices; generally individuality and dissent are stoppered. Usually propaganda is utilized to convince the masses, and a healthy dose of fear is used to brainwash citizens into believing that any other way would be disastrous.
In the case of 1984, the traits that apply are: the restriction of information, independent thought, and freedom; constant surveillance; fear of punitive response to individuality or dissent; uniform expectations; and of course, the protagonist feels trapped and questions the systems in place. Thoughtcrime and Newspeak are specific examples from the text that indicate totalitarian control over the characters.