Brucie's answer is the best one, I think - it cuts deeper than external accoutrements like qualifications or even skill.

But I was niggled by GUEST,KJ's statement: "Anybody that says 'it doesn't matter, it's only folk'!! is not a musician in my book".

That is an aggressive stance, but it may be right. I am sure the Copper Family never thought of themselves as musicians; after all, they all had day jobs to sustain them. Neither would Cecil Sharp have. Yet who has made a bigger impact on English traditional music that the Coppers or Cecil? My point is: Being a "musician" is not necessary to make an impact in the world of music.

"Musician" is a label, that's all. It confers no rights, is no qualification - just a description.