"Mamma Mia!" group (4)
I believe the answer is:
abba
'mamma mia group' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for abba that I've seen before include "Enclosed rhyme" , "Eurovision prizewinning Swedish pop group" , "Father (NT)" , "striped coat?" , "They used to record" .)