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。