joke vs in-joke

joke and in-joke both are nouns.

Word	Noun	Adjective	Verb	Adverb
joke	Yes	No	Yes	No
in-joke	Yes	No	No	No

As nouns, in-joke is a hyponym of joke; that is, in-joke is a word with a more specific, narrower meaning than joke:

joke: a humorous anecdote or remark intended to provoke laughter
in-joke: a joke that is appreciated only by members of some particular group of people

joke (noun)	in-joke (noun)
a ludicrous or grotesque act done for fun and amusement	a joke that is appreciated only by members of some particular group of people
activity characterized by good humor
a triviality not to be taken seriously
a humorous anecdote or remark intended to provoke laughter

joke (verb)	in-joke (verb)
act in a funny or teasing way
tell a joke; speak humorously