O'Sullivan introducing party piece? (5)
I believe the answer is:
rondo
'piece?' is the definition.
(type of musical composition)
'o'sullivan introducing party' is the wordplay.
'o'sullivan' becomes 'ron' (I can't justify this - if you can you should give a lot more credence to this answer).
'introducing' means one lot of letters go next to another (some letters go before others).
'party' becomes 'do' (do is a kind of party).
'ron'+'do'='RONDO'
Can you help me to learn more?
(Other definitions for rondo that I've seen before include "Music with repeated refrains" , "has repetitive theme" , "part of a sonata" , "Piece in the form of a sonata's last movement, say" , "Musical form with recurring theme" .)