Shaking butts, couple of fellows dance (3-3)
I believe the answer is:
cha-cha
'dance' is the definition.
(I know that cha-cha is a kind of dance)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for cha-cha that I've seen before include "Latin-American dance" , "Modern ballroom dance from Latin America" , "certain steps" , "Latin American ballroom dance" , "Repetitive Latin American dance" .)