folk ballad vs folk song

folk ballad and folk song both are nouns.

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

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

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

Other synonyms of folk ballad include folksong.

folk ballad (noun)	folk song (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