The way rounds are labeled are stupid, going back and forth between metric and standard measurements.
"9mm" or more appropriately 9mm Luger OR 9mm Parabellum (same thing different name LOL!) measures out to 9x19, or 9mm in diameter and 19mm in length.
Then you have 9x18 Makarov, which is a Comm-Bloc round (think USSR)
Next in line is .380, which some people call 9mm Short, which is kind of a stupid term seeing how you still have the Mak round below 9mm Luger. .380 is 9x17, which makes it still a 9mm round, just with less oomph.
I told you it's stupid.