Real difference between BAPI and RFC

Dear All,

I have read several threads addressing the difference between BAPI and RFC, but I am not convinced with the explanations(like all BAPI are RFCs and vice-versa is not true, and most posts simple explain what a BAPI or RFC is). I believe there is a critical difference between the two, which the threads/posts have missed out. I would be glad if someone can answer bring this out.

Thanks in Advance,

Rajesh