Why is there a macro which defines _tmain?

Question

I am new to C++ coding, coming from Java and C# background. I'm puzzled by the proliferation of #define terms starting with the most basic:

#define _tmain wmain

When I first learned a smattering of C ages ago, the main function was:

int main(int argc, char *argv[])

In the Visual C++ project I created, it made the main function:

int _tmain(int argc, _TCHAR* argv[])

I'm just wondering why there needed to be a name translation from wmain to _tmain? Why not just use the original C main function prototype?

In general there seems to be lot of #define renaming something which looks pretty clear to start with, to something which looks more mysterious and less clear (I mean wmain to _tmain ??).

Thanks for tolerating what may be a very obvious question.