What do you call cheese that's not yours?
Q: What do you call cheese that's not yours?
A: Nacho cheese.
This is a moderately common joke. The reason why it is funny is because "Nacho cheese" is a real type of cheese, and it also sounds like the words "Not yo' cheese", which is slang for "Not your cheese". Both of these possible answers could be considered correct for this question. This is a pun. In this joke, the joke is the fact that the person that says it is saying something that sounds like two possible answers at the same time.