A .38 or a .357 magnum are both .357. The .357 case is longer, and holds more powder for more power.
The .380 is a european calibre. It is actually called 9mm kurtz. it is .355 just like the longer more powerful 9mm parabellum (9mm Luger).
Dont even think about the other members of the family like the .38 Super or .357 SIG. That is when it gets very complicated.
SO9