folk song vs folk ballad

folk song and folk ballad both are nouns.

Word	Noun	Adjective	Verb	Adverb
folk song	Yes	No	No	No
folk ballad	Yes	No	No	No

As nouns, folk song and folk ballad are synonyms defined as:

folk song and folk ballad: a song that is traditionally sung by the common people of a region and forms part of their culture

Other synonyms of folk song include folksong.

folk song (noun)	folk ballad (noun)
a song that is traditionally sung by the common people of a region and forms part of their culture	a song that is traditionally sung by the common people of a region and forms part of their culture