What does the flag -m modules do?

[JulianS-Uni]

Like the title says, can someone explain me what the purpose of this flag is?

-m module, --module module
                        Python module(s) containing symbols which will be
                        imported instead of generated

Maybe provide a example? I have a header i want to clang2py with windows types like WORD or PVOID. I thought i can import them with -m ctypes.wintypes but that does not seem to be the case.