Films some developed, about six (6)
I believe the answer is:
movies
'films' is the definition.
('movie' can be a synonym of 'film')
'some developed about six' is the wordplay.
'developed' indicates an anagram.
'about' indicates putting letters inside.
'six' becomes 'VI' (Roman numerals).
'some' anagrammed gives 'moes'.
'moes' going around 'vi' is 'MOVIES'.
(Other definitions for movies that I've seen before include "Informally, films shown in cinemas" , "Motion pictures" , "Flicks" , "Cinema films" , "Films in America" .)