Sheep around trap's edge (6)
I believe the answer is:
margin
'edge' is the definition.
(I know that margin is a type of edge)
'sheep around trap's' is the wordplay.
'sheep' becomes 'ram' (male sheep).
'around' is a reversal indicator.
'trap' becomes 'gin' (gin trap is a kind of animal trap).
'ram' written backwards gives 'mar'.
'mar'+'gin'='MARGIN'
(Other definitions for margin that I've seen before include "Edge, border, fringe" , "Permissible difference" , "Blank space that surrounds the text on a page" , "Bound" , "Boundary line or the area" .)