In joke
An in-joke is a joke whose humour is only clear to those people who are "in" a group which has some prior knowledge (not known by the whole population) which makes the joke thus humorous. Also called an "inside joke."This group of people could be, e.g.:
- a nuclear family or (parts of) an extended family
- just a few people who work together
- people of the same vocation or profession
- residents of a particular town or region
- viewers of a particular television series or cult movie
- readers of a particular book or series of books
- users of the same computer or computer software