To me, folk music is what I define it to be.

To you, folk music is what you define it to be.

Some of what I think is folk music, you also think is folk music, but some of what I think is folk music, you don't think is folk music. And vice versa.

There's no problem with that, until I mention something that I think is folk music, and you don't think is folk music. Then we get into a bloody great argument. So it's best not to ask what folk music is, but as others have said, just enjoy listening to it and playing or singing it.

:-)