folk ballad vs fado

folk ballad and fado both are nouns.

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

As nouns, fado is a hyponym of folk ballad; that is, fado is a word with a more specific, narrower meaning than folk ballad:

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

Other hyponyms of folk ballad include blues.

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