The 1954 definition is the only serious attempt (AFAIK) to give a meaning to the terms "folk music" or "folk song" that is harmonious with "folk art" "folk tale" "folk myth" "folklore" or "folkways" and indeed foreign expressions such as "volkslieder" or "folklorique".

Since a folksong may remain a folksong even if done in reggae or as folk-rock or as folk-metal (or some of those hideous versions of Barb'ra Ellen with tightly corseted contralto and grand piaaaaaano) it is plain that a meaning based on manner of performance, or style is untenable. The obvious other avenues to giving the word "folk" a meaning in this context are derivation and/or currency. It appears to me that the 1954 definition neatly uses both, and is more consistent with the term "the folk" as in "the people" which would tend to be backward looking (in a sense of time) and to include a sense of duration and history, so to exclude the flash mob (and purveyors of social worker psychobabble).

In short, it is the best definition of folk music and song of which I am aware.

Oh shit, another "what is folk" thread - but I suspect the OP intended that.