not such a stupid question, because in Europe .380 ACP is often referred to as '9mm short' or '9mm Kurtz'. It's 9x17. Then there's '9mm Mak' which is 9x18.
In Italy we have also 9x21, alias 9mm IMI, because 9x21 is condidered a military bullet, thus reserved to the police/army. And yes, 9x21 is pratically the same thing.