Musical foursome going up or down (4)
I believe the answer is:
abba
'up or down' is the definition.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for abba that I've seen before include "famous pop group" , "Old group" , "Group - father" , "rhymes in Petrarchan sonnet" , "camel-hair coat" .)