Definition of "in-joke" [in-joke]

• Informal A joke originated or appreciated by the members of a particular group. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Why so funny/clever, well Chaim Potok's best known novel is "The Chosen", obscure but it made me chuckle in a sort of "I get the in-joke" way."
• "Nothing like getting an in-joke five damn years later."
• "On ITV, a new series of Taggart investigates a mutilated medic found in a warehouse, while over on Channel 5, CSI comes out fighting, kicking off season 11 in explosive fashion: there's a bombing at a funeral, a sexy new English technician and a knockout blow in the shape of singing fingerpuppet Justin Bieber, who guest stars in an episode called Shock Waves – possibly some kind of in-joke about hair products."