For me, the only definition that is practically of value, is that a folk song should be one that anyone can sing easily and with enjoyment.

Most modern "pop" songs are actually quite difficult to sing (and are instantly forgettable as they are often written to a formula.

A traditional folk song is one that has been sung repeatedly for a period of time, lets say 50 years as a arbitrary number. This means that a number of people have liked it well enough to keep singing it and that its appeal has not been limited to a specific period in time.

Personally I don't care what the style of music is...

However I do like to feel I am singing something that sprang from our own land. I have sung more than enough African, Georgian etc etc in my time.