“Great goal” is all you’ll hear a girl raving (4,5)
I believe the answer is:
holy grail
'great goal is all you'll' is the definition.
I can't tell whether this definition defines the answer.
'hear a girl raving' is the wordplay.
'hear' becomes 'holy' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'raving' indicates an anagram.
'a'+'girl'='agirl'
'agirl' anagrammed gives 'grail'.
'holy'+'grail'='HOLY GRAIL'
Can you help me to learn more?
(Other definitions for holy grail that I've seen before include "object of quest" , "Go, Hillary! (anag) -- chalice used by Jesus at the Last Supper" , "Cup that was much sought after?" , "Chalice used by Christ at the Last Supper" , "A cherished ambition" .)