The music doesn't require an authoritative definition. It's a subset of individuals who participate in the music who require a definition. They aren't the music, they're just people who play it, sing it, or listen to it. They require authoritative sources not for edification, but to validate and corroborate the opinions they already hold. Nevermind that, in most cases, an equally authoritative source can be found to validate and corroborate any other opinion on the subject.