What is knock that Americans often say in movies?

Knock-knock joke is an English joke often told by European and American children. Pun, as a pun, generally consists of two people answering each other. A standard knocking joke consists of five sentences:

A: Knock, knock! (Knock knock! )

B: Who's there? (Who is it? )

A: X. (X can be an object or a person's name)

B: X Who? (who is x? /Which X? )

A: joking with puns.

Word explanation

Knock is an English word, noun and verb, which means "knocking" when used as a noun; Knock on the door; When used as a transitive verb, it means "knocking at the door"; Fight; Knock on the door; "Criticism", when used as an intransitive verb, means "knocking; Fight; Knock on the door. "

Example: Knock at the door first, and then wait to be invited in.

You should knock at the door first, and then wait for the invitation to enter.