A pop group holds record (5)
I believe the answer is:
alpha
'a' is the definition.
(the Greek letter A)
'pop group holds record' is the wordplay.
'pop group' becomes 'A-ha'.
'holds' is an insertion indicator.
'record' becomes 'L-P' (abbreviation for long play record).
'aha' going around 'lp' is 'ALPHA'.
(Other definitions for alpha that I've seen before include "starter" , "A for Aristophanes!" , "Foreign character" , "European character" , "piece of Greek writing" .)