What is "knock-knock joke"

alt. One of a class of childish jokes told as a dialog, and usually including a pun, in the following form: n. One of a class of childish jokes told as a dialog, and usually including a pun, in the following form:

The knock-knock joke is a type of joke, in the format of "call and response", where the response contains a pun.

The standard format has five lines:

1. The punster: Knock, knock!
2. The recipient: Who's there?
3. The punster: a variable response, sometimes involving a name.
4. The recipient: a repetition of the response followed by who?
5. The punster: the punch line, which typically involves a pun-based misusage of the word set up during the response (How did you know?)

For example:

1. The punster: Knock, knock!
2. The recipient: Who's there?
3. The punster: Woo.
4. The recipient: Woo who?
5. The punster: Don't get excited. It's just a joke.