朋友聚会的时候，有人说了个，可只有几个人相视而笑，其他人都面面相觑，不知所以然。这种情况大都是因为那个笑话跟他们几个人都知道的某件事有关，所以只有他们才能明白其中的可笑之处。这种笑话就叫做in-joke。
An in-joke, also known as an inside joke or in joke, is a joke whose
humor is clear only to people who are in a particular social group, occupation, or other community of common understanding; an esoteric joke. It is humorous only to those who know the situation behind it.
In-joke （也叫inside joke或in joke）是只有在同一个社交圈子、职业或者思维理解方式一致的群体内才明白的幽默，即“圈内人的幽默”。只有那些了解事件背景的人才能明白其中的幽默之处。
For example:We have an in-joke; whenever someone sings
a wrong note, they wipe the mistake off their music with an obvious gesture.
我们内部有个搞笑惯例，每次有人唱错了，他们就用一个特别明显的手势把这个错误给抹掉。