In-joke

An in-joke is like a secret joke that only some people understand. It's like when you and your friends have a special word or make a funny face that you only do with each other. Only you and your friends know what it means and why it's funny. That's an in-joke! It's usually something that happens or is said repeatedly, so you all remember it and can laugh about it together. It's like having your own special club that only people who know the joke can be a part of.