By whom?
Is a .357 30 Caliber? .375?
I think that it's fairly safe to say that many people, myself included, think of cartridges in "family groups." One way might be in the development, say that the 25/06, .270 Winchester, .280 Remington, and the 30/06 being in the same family, since they "sprung from" the same (30/06) cartridge. On the other hand, (again, myself included) also group families by the nearly identical bullet diameters. So just as I would consider the 9mm Luger, .38 special, and .357 all in the 9mm family (.355 - .357), I'd consider the .30 Carbine, 7.62x39, 30-30 Winchester, 7.62 NATO, and 30/06 all "30 caliber" rounds, even though they're all completely different in ballistics and dimensions. The .375 wouldn't fit well in the group.
Mark
It may be one of those "gun" things.
In the reloading manual universe the family groups are fairly big with just the bullet diameter. Expanding into multiple bullet diameters can make things really unwieldy. Though I just learned how treacherous things can be with the .303 British.
There was a pretty good food fight on another thread a while back about the proper nomenclature for the .45 pistol cartridge.
The poster of the first part insisted the proper industry term was .45 ACP while the poster of the second part said .45 Auto was equally acceptable.
You can find commercially available ammo from reputable companies with either term printed on the box.
I stayed out of that particular kerfuffle.
Best regards,