Stereotype
A stereotype is a mistaken idea or belief many people have about a thing or group that is based upon how they look on the outside, which may be untrue or only partly true. Stereotyping people is usually considered a type of prejudice because how a person would appear on the outside is a small part of who a person is on the inside. Like other untrue opinions, stereotypes might be used as reasons to discriminate against another person, or sometimes for a humorous effect in fiction.