The answer depends on the context. One common context is discussions about availability of ammunition, in which case 9mm, .40, 5.56mm, 7.62mm, and 12 gauge are about it (in the US), with .45ACP and .38 special on the fringe.
The other context is discussing a band of power in the handgun calibers, running from 9mm through .40 and ending at .45ACP; .38Spl+P can fit on that band as well. Cartridges along that band generally offer equivalent value, with tradeoffs between greater momentum versus greater energy, and arguably slight tradeoffs between capacity versus single-shot-performance. One can make a strong argument that a choice between cartridges on this band is really a question of taste, not different capabilities. This is a useful context if you're trying to distinguish between these "service calibers" and things that are a clear step down (e.g., .380, .32 ACP) or a clear step up (10mm, .41 magnum). Some would quibble over whether a .357 is enough of a step up to be in the next band; I think it is, but the "bullets below 2000 fps just poke holes" crowd might not concede that.