scat singing vs singing

scat singing and singing both are nouns.

Word	Noun	Adjective	Verb	Adverb
scat singing	Yes	No	No	No
singing	Yes	Yes	No	No

As nouns, singing is a hypernym of scat singing; that is, singing is a word with a broader meaning than scat singing:

scat singing: singing jazz; the singer substitutes nonsense syllables for the words of the song and tries to sound like a musical instrument
singing: the act of singing vocal music

Other hypernyms of scat singing include vocalizing, jazz.

scat singing (noun)	singing (noun)
singing jazz; the singer substitutes nonsense syllables for the words of the song and tries to sound like a musical instrument	the act of singing vocal music
	disclosing information or giving evidence about another

scat singing (adjective)	singing (adjective)
	smooth and flowing