A mince pie is an art form (6)
I believe the answer is:
cinema
'an art form' is the definition.
'a mince pie' is the wordplay.
'pie' indicates an anagram.
'a'+'mince'='amince'
'amince' with letters rearranged gives 'CINEMA'.
'is' acts as a link.
(Other definitions for cinema that I've seen before include "Films, collectively" , "place for pictures" , "(Building for) film" , "Picture-house 96)" , "Silver screen" .)