Pigs displayed covered tails (7)
I believe the answer is:
shadows
'tails' is the definition.
('shadow' can be a synonym of 'tail')
'pigs displayed covered' is the wordplay.
'pigs' becomes 'sows' (I've seen this before).
'displayed' becomes 'had' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'covered' is an insertion indicator.
'sows' placed around 'had' is 'SHADOWS'.
Can you help me to learn more?
(Other definitions for shadows that I've seen before include "1960s band" , "tracks" , "Dogs" , "Follows" , "Dark areas where the light is blocked" .)