What is the difference between a Post Graduate Degree and MS degree?

In the US and many other countries, an MS (Master of Science) degree *is* a type of postgraduate degree. The terms aren't mutually exclusive. A postgraduate degree is a broad umbrella term encompassing any degree pursued *after* a bachelor's degree. This includes:

* Master's degrees: MS, MA (Master of Arts), MBA (Master of Business Administration), MFA (Master of Fine Arts), etc. These are all postgraduate degrees.

* Doctoral degrees: PhD (Doctor of Philosophy), EdD (Doctor of Education), etc. These are also postgraduate degrees.

* Professional degrees: These are often postgraduate and might have their own unique titles (like a Master of Public Health or a Juris Doctor).

So, an MS degree is a *specific kind* of postgraduate degree. All MS degrees are postgraduate, but not all postgraduate degrees are MS degrees.