In-joke


An in-joke, also known as an inside joke or a private joke, is a joke whose humour is understandable only to members of an ingroup, that is, people who are in a particular social group, occupation, or other community of shared interest. It is an joke, i.e., it is humorous only to those who are aware of the circumstances behind it.
In-jokes may exist within a small social clique, such as a group of friends, or extend to an entire profession. An example is:
This joke is so esoteric that most outsiders could not even confidently guess to which group it might be funny, let alone why. In fact, it is a mathematics joke,
a pun on the name of a famous result, Zorn's Lemma.
Ethnic or religious groups may also have their own in-jokes.

Philosophy

In-jokes are cryptic allusions to shared common ground that act as triggers; only those who have shared the common ground provide an appropriate response.
An in-joke works to build community, sometimes at the expense of outsiders. Part of the power of an in-joke is that its audience knows that there are those who do not understand the joke.
An in-joke can also be used as a subtext, where people in the know may find humour in something not explicitly spoken. They may even apologize for doing so to a rookie, directly or indirectly stating that what they were laughing at was an in-joke.