An in-joke, also known as an inside joke or in joke, is a joke whose humour is clear only to people who are in a particular social group, occupation, or other community of common understanding. It is an esoteric joke which is humorous only to those who know the situation behind it.
In-jokes may exist within a small social clique, such as a group of friends, or extend to an entire profession such as the film or professional wrestling industries, or a particular sporting endeavour. Even an ethnic or religious group may have its own in-jokes.
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 with something not explicitly spoken. They may even apologise for doing so to outsiders, directly or indirectly stating that what they were laughing at was an in-joke.
Computer industry 
In the computer industry some computer programmers hide in-jokes within the code of software in the form of Easter eggs, i.e., hidden content that can be revealed only by following a specific sequence of inputs.
The Jargon File is a glossary of hacker slang, much of which is in-jokes or is based on in-jokes.
Pop culture 
Many TV shows, like The Simpsons and Family Guy, insert numerous in-jokes per episode, often referring to other TV shows, movies, or even the show itself.
The 2009 movie Star Trek contained multiple references to the 1960s Star Trek TV series, with the references constituting in-jokes for those familiar with the series.
Noticeable in many animated films is A113, a classroom used by graphic design students at CalArts, whose alumni include John Lasseter and Brad Bird.
The Wilhelm Scream is a notable in-joke that has appeared in over 200 different movies, TV shows, and video games.
See also 
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Killing Joke - In Cythera
Music video by Killing Joke performing In Cythera. (C) 2012 Spin-Farm Oy, Under Exlusive Licence From Various Artists Management.
Monty Python - The Funniest Joke In The World
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New York Daily News
New York Daily News
Wed, 24 Apr 2013 14:27:06 -0700
A Tennessee state senator is being slammed for insensitivity to the Boston Marathon bombing victims after posting an illustration of a pressure cooker – like the ones used in last week's deadly attack – to mock gun control advocates. Republican Stacey ...
Sun, 28 Apr 2013 06:55:37 -0700
In joke fest, Obama mocks himself, rivals. He's not 'the strapping young Muslim socialist' he used to be, the president muses at the annual White House Correspondents' Association dinner Saturday. By BRADLEY KLAPPER The Associated Press ...
Houston Chronicle (blog)
Thu, 23 May 2013 12:37:06 -0700
Add some fried chicken-skin cracklings for crunch (a little gribenes in-joke ), pile the results on a serious wheat bun flecked with oats, and you end up with the most interesting chicken salad sandwich around. If it sounds like you might want to try ...
Thu, 23 May 2013 13:51:19 -0700
It builds upon one of the best television pilots ever created, layering in joke upon joke upon joke, so that some character beats – such as G.O.B. (Will Arnett) and his assumed affinity for murdering small animals – end up paying off for the series ...
Deutsche Welle (press release)
Wed, 15 May 2013 15:27:01 -0700
The in-joke in the Swedish music industry is that its composers are as successful as Ikea. Not only is the Scandinavian country a multiple European Song Contest title-holder, it also provides other countries with hits. As seven-time champion, Ireland ...
Norfolk Daily News
Thu, 23 May 2013 09:19:50 -0700
“Name your price,” Johnson replies to conclude what can only have been an in-joke by those responsible for a series that, through five films, has grossed $1.5 billion and still looks to be gaining speed globally. This new entry will only add mightily ...
The Chicago Maroon
The Chicago Maroon
Tue, 21 May 2013 00:25:46 -0700
This song was the perfect note on which to end: a massive in-joke that simultaneously expressed both love for the show and frustration with the need to move on to careers with less artistic freedom and more economic comfort. Because that's precisely ...
Wed, 22 May 2013 06:16:14 -0700
He began re-watching the episodes about six months ago, carefully cataloging and taxonomizing every in-joke, pun and visual gag. At first, he said, he'd have to pause episodes frequently, but eventually it “became easier to be a humorless statistician ...
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