" left wing approach"
Why "left wing"
I met Charles Seeger several times - I got the impression that he was as left wing as Bert, even more so
"Does it have a hard and fast definition? "
It defines a long-dead phenomenon so it can only be redefined by adding fresh information
You can't re-deine the plays of shakespeare ot Elizabethan madrigals - why should you be able to re-deinne folk songs
If folk song creation should miraculously rise from the dead, that would be a different matter
You have attempted to do the equivalent of Shakespearean plays by throwing the works of Johnson, Webster, Beumonont and Fletcher et al into the mix
Jim