Definition of "folksong"

The fireman jumped, but Casey Jones stayed to blow the whistle to give the goods train crew time to escape. His sacrifice is commemorated in an American folksong.

1950 June, “Casey Jones Stamp”, in Railway Magazine, page 420

For the former a folksong or a folkdance was a mere source for a composition, artistic arrangement, or stylization; for the latter it was important to respect the style of the traditional singer […]

2012, Ian Peddie, Popular Music and Human Rights: British and American Music, page 80