What is an ingrown hair on a butt called?

There isn't a specific, widely used term for an ingrown hair on the buttocks.

While "ingrown hair" is the general term, you could use a more descriptive term like:

* Ingrown hair on the buttock(s)

* Ingrown hair on the buttocks

* Ingrown hair in the gluteal region

It's important to be mindful of context and audience when discussing sensitive topics like this. Using more clinical or anatomical terms might be more appropriate in certain situations.