inside joke

: an interior or internal part or place : the part within

: inward nature, thoughts, or feeling

: viscera, entrails

: on the inner side

: in or into the interior

: to or on the inside

: of, relating to, or being on or near the inside

: relating or known to a select group

: behind-the-scenes

: in or into or as if in or into the interior of

: on the inner side of

: within

: something said or done to provoke laughter

: the humorous or ridiculous element in something

: an instance of jesting : kidding

: to make jokes : jest

: to make the object of a joke : kid