Films some developed, about six (6)
I believe the answer is:
movies
'films' is the definition.
(I know this)
'some developed about six' is the wordplay.
'developed' indicates an anagram.
'about' means one lot of letters goes inside another.
'six' becomes 'VI' (Roman numerals).
'some' is an anagram of 'moes'.
'moes' placed 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" .)