A poser about musical dramas (6)
I believe the answer is:
operas
'musical dramas' is the definition.
(I've seen this before)
'a poser about' is the wordplay.
'about' indicates an anagram.
'a'+'poser'='aposer'
'aposer' anagrammed gives 'OPERAS'.
(Other definitions for operas that I've seen before include "Musical works" , "La Traviata, Aida" , "Musical plays" , "'La Boheme and La Traviata, say (6)'" , "These shows are a poser, oddly" .)