Having thought about this question for a number of years I've come out with my definition. Folk music is accessible to people. That's why it reaches so many.
When it becomes esoteric or rarified it loses its meaning. It's generally a simple musical statement without being simplistic. It's unaffected. Academics have tried unsuccessfully to define it. Record companies have also. It is always redolent of where it came from, a cultural base. It may not be popular now but it will go on when all popular trends in music have disappeared. Why? Because we need it. It tells us who we are.

The time has come like democracy for people to reclaim it.

It defines itself.