Here’s a surprise about the French overture from Ravel? It’s not an overture (6)
I believe the answer is:
bolero
'it's not an overture' is the definition.
(type of song)
'here's a surprise about the french overture from ravel?' is the wordplay.
'here's a surprise' becomes 'boo' (boo!).
'about' means one lot of letters goes inside another.
'the french' becomes 'le' ('the' in French).
'overture from' suggests taking the first letters (the introduction or overture to the word).
The initial letter of 'ravel' is 'r'.
'le'+'r'='ler'
'boo' enclosing 'ler' is 'BOLERO'.
(Other definitions for bolero that I've seen before include "what Ravel wrote" , "Ravel piece; a jacket" , "Lively Spanish dance" , "Kind of jacket or dramatic music by Ravel" , "Rob Leo of his strange jacket" .)