ballad vs song

ballad and song both are nouns.

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

As nouns, song is a hypernym of ballad; that is, song is a word with a broader meaning than ballad:

Other hypernyms of ballad include vocal.

ballad (noun)	song (noun)
a narrative poem of popular origin	the act of singing
a narrative song with a recurrent refrain	a short musical composition with words
	the characteristic sound produced by a bird
	a distinctive or characteristic sound
	a very small sum