A "Knock Knock Joke" is a type of humor that typically involves a call-and-response format. It starts with one person saying "Knock, knock," to which the other person responds, "Who's there?" This exchange sets up the punchline, which usually involves a play on words or a pun. These jokes are often simple and suitable for all ages, making them popular among children. The structure allows for creativity, as the setup can lead to various humorous outcomes. Common themes include animals, food, or everyday objects, making them relatable and easy to remember.