what is BOOL WINAPI return type

I came across a function definition in c++ as follows: (source)

BOOL WINAPI GetProcessMemoryInfo(
  _In_   HANDLE Process,
  _Out_  PPROCESS_MEMORY_COUNTERS ppsmemCounters,
  _In_   DWORD cb
);

What is the return type here. Is it BOOL WINAPI or BOOL? Where is this type defined?