A knock-knock joke is a type of humor that typically involves a call-and-response format. One person starts by saying "knock, knock," prompting the other person to ask, "Who's there?" This exchange continues with the first person providing a name or phrase, leading to a punchline that often involves a pun or play on words. These jokes are popular among children and adults alike due to their simple structure and playful nature. They often rely on wordplay, making them easy to remember and share. Knock-knock jokes are a fun way to engage in lighthearted conversation and laughter.