When your back and your butt welds in to each other.
It oftens happens when people are tall and skinny, so they have no butt but a long back and it looks like they are togheter.
* Its not called "no but" honey, they are called Backeteérs!
* It means that he has a small butt that is in a equal line as the back.
- Aaaah, i see a Back Butt combination will be a Backeteér.