"Duh" is an informal expression often used to indicate that something is obvious or self-evident. It can convey a sense of annoyance or disbelief when someone states something that the speaker considers common knowledge. The term is frequently used in casual conversations and can be accompanied by a tone of sarcasm. The origin of "duh" is believed to stem from the early 20th century, gaining popularity in the 1960s and 1970s. It is commonly associated with youth culture and is often used in media, including television shows and movies, to emphasize a character's frustration or exasperation with another's lack of awareness.