Jazzy improv style (4)
I believe the answer is:
scat
'jazzy improv style' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for scat that I've seen before include "Type of jazz singing - be off!" , "Wordless jazz singing" , "One way of singing" , ""Beat It"" , "way to sing > "Go away!"" .)