Business star about to manage light work (5,5)
I believe the answer is:
comic opera
'light work' is the definition.
(type of light or trivial work)
'business star about to manage' is the wordplay.
'business' becomes 'co' (short for company).
'star' becomes 'mira' (star in the constellation Cetus).
'about' means one lot of letters goes inside another.
'to manage' becomes 'cope' (manage can mean to cope or do well).
'mira' going around 'cope' is 'micopera'.
'co'+'micopera'='COMIC OPERA'
(Other definitions for comic opera that I've seen before include "Light work" , "Something by Offenbach" , "It has dialogue as well as singing" , "Milton perhaps" , "many will laugh at that" .)