Pop singers climbing or descending (4)

I believe the answer is:

abba

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'pop' is the definition.
(I have seen 'Biblical pop' mean 'abba' so perhaps 'pop' could also mean 'abba')

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for abba that I've seen before include "Palindromic Swedish pop group who sang ` `Waterloo' '" , "Palindromic 70s pop group" , "Pater's" , "Group winning the 1974 Eurovision Song Contest in Brighton" , "1970s Swedish pop group" .)

I've seen this clue in the Sydney Morning Herald.

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