Knock-knock jokes are a popular form of humor that typically involve a call-and-response format. They start with one person saying "Knock, knock," to which the other person responds, "Who's there?" This exchange sets the stage for a pun or play on words, leading to a punchline that often elicits laughter. These jokes are simple and can be enjoyed by people of all ages, making them a favorite among children. The structure is easy to remember, allowing anyone to create their own variations. Overall, knock-knock jokes are a fun way to engage in lighthearted conversation.