Anything can be defined, though not perfectly for all contexts amd certainly not finally and for all time.

The issue isn't whether "folksong" (or "folk," which is a bit different) is definable, it's how well the definition explains what most people seem to mean when they use the word.

The two dictionary definitions I offered seem to me to cover the possibilities well enough for everyday use. (They're definitions, not encyclopedia articles.) It's unfortunate that they describe two different, even contrasting, phenomena (trad songs and songs "inspired" by them), but they do. That's how the words are actually used, and have been for at least fifty or sixty years.

But posters here aren't just interested in *the* definition of "folksong" (which demands that there be just one); they're equally exercised about what specific songs "deserve" the coveted "folk" label. And clearly it is coveted. (Another word whose meaning has expanded, though less obviously, in recent decades.)

Labeling isn't a matter of definition but of application. The gray area, which hardly existed 150 years ago, is now - because of the commercial definition of "folksong" - quite enormous. To that extent it's a futile discussion.