inside joke(redirected from an inside joke)
A joke that is amusing to certain people but is not readily understandable or humorous to others. Oh, they're all giggling over some stupid inside joke. It's an inside joke, Mom—you wouldn't get it.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a joke that only certain people understand; a joke understood only by people who know certain facts and context. What you said must be an inside joke. It makes no sense to me.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.