Clinton, what I've heard is that "Celtic" refers to places where Celtic languages were/are spoken, and is based on cultural factors, not genetic ones. Of course, it does illustrate how the word may not be very useful, because the word means different things to different people. Some people think "Celtic" is a type of music originating with the Celts, and has been handed down and changed over the centuries to be come modern Irish/Scots/etc music. Some people think if you're from a "Celtic" nation, anything you play is "Celtic." Others may not know what the heck you're talking about. They may assume they understand, but be wrong.