As the saying goes "A map is not the territory"

Maps help you get to some places and avoid others, and that matters; and the same is true of terms like "folk music". It's important that maps and words should be consistent and easy to understand. They involve making use of conventions which are in a sense arbitrary, but if they are used arbitrarily they cease to be useful as a guide.

But what really matters is the territory represented by the map, and the music identified by the terms.