Musical form with runs about note (5)
I believe the answer is:
rondo
'musical form' is the definition.
(I've seen this before)
'with runs about note' is the wordplay.
'with' means one lot of letters go next to another.
'runs about' becomes 'ron' (I am not sure about this - if you are sure you should believe this answer much more).
'note' becomes 'do' (musical note, as in do-re-mi).
'ron'+'do' is 'RONDO'.
Can you help me to learn more?
(Other definitions for rondo that I've seen before include "part of a sonata" , "Musical piece with returning theme" , "Music form with repeating theme" , "noted work" , "Repetitive musical form" .)