scat singing

n. singing in which the singer replaces improvised gibberish syllables for the words of a song and attempts to sound like a musical instrument (in Jazz singing)

Scat singing is a type of voice instrumental music. A scat is vocalized either wordlessly or with nonsense words and syllables (e.g. "bippity-bippity-doo-wop-razzamatazz-skoobie-doobie-bee-bop-a-lula-shabazz") as employed by jazz singers. Scat singing gives singers the ability to sing improvised melodies and rhythms, to create the equivalent of an instrumental solo using their voice.
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Noun
1. singing jazz; the singer substitutes nonsense syllables for the words of the song and tries to sound like a musical instrument
(synonym) scat
(hypernym) singing, vocalizing