Southern gallery keeps high-class sculpture (6)
I believe the answer is:
statue
'sculpture' is the definition.
(I know that statue is a type of sculpture)
'southern gallery keeps high-class' is the wordplay.
'southern' becomes 's' (abbreviation).
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
'keeps' is an insertion indicator.
'high class' becomes 'U' (as in U and non-U speech).
'tate' enclosing 'u' is 'tatue'.
's'+'tatue'='STATUE'
(Other definitions for statue that I've seen before include "One representing liberty" , "permanent fixture" , "A carved image or effigy" , "Piece of sculpture" , "Sculptured likeness" .)