in-joke vs joke

in-joke and joke both are nouns.

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

As nouns, joke is a hypernym of in-joke; that is, joke is a word with a broader meaning than in-joke:

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

Other hypernyms of in-joke include gag, jape, jest, laugh.

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

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