Wikipedia usually has a serviceable writeup on most ammo calibers. The nomenclature can be confusing, especially with foreign-made guns and ammo, and lots of folks get confused.
I have two Czech-made CZ 83s, one in .380 ACP and the other in .32 ACP. Their slides state their calibers are 9 Browning Court and 7.65 Browning, respectively.
After buying a pistol chambered in 9 Luger (aka 9 Parabellum or 9x19), I walked into a sporting goods store in search of ammo. The elderly sales clerk told me he had no 9mm ammo, except for some 9mm Short that I could shoot in my new gun. He showed me a box of .380 ACP. I told him that was an entirely different caliber, and he eyed me suspiciously.
I have a CZ 82, which is chambered in 9 Makarov. I went into a gun store once and bought a couple of boxes each of 9 Makarov and 9 Luger. The clerk looked at me in horror and asked if I knew they were different and can't be used in the same gun. I calmly nodded that I did, but I think he thought I was too proud to admit an error. My guess is he sees a fair number of folks buying the wrong stuff.
Not that all 9mm calibers have the exact same diameter, but they are nominally that wide. Interestingly, the most common nominal handgun caliber is 9mm by far. Wikipedia lists more than 30:
https://en.m.wikipedia.org/wiki/9_mm_caliber. Compare that to 15 such calibers around 10mm, and only 8 around 8mm. Could that be because 9mm is the optimal nominal caliber for a service sidearm?