Encouraging holding copies back -- that's mean (12)
I believe the answer is:
cheeseparing
'mean' is the definition.
(I've seen this before)
'encouraging holding copies back' is the wordplay.
'encouraging' becomes 'cheering' (cheering is a kind of encouraging**).
'holding' means one lot of letters goes inside another.
'copies' becomes 'apes' ('ape' can be a synonym of 'copy').
'back' says the letters should be written backwards.
'apes' backwards is 'sepa'.
'cheering' enclosing 'sepa' is 'CHEESEPARING'.
'that's' acts as a link.
(Other definitions for cheeseparing that I've seen before include "Close" , "parsimonious behaviour" , "Mean with money" , "Penny-pinching" , "Stinginess" .)