Scrap rotten bit of meat (6)
I believe the answer is:
offcut
'scrap' is the definition.
(offcut can mean a scrap or leftover piece)
'rotten bit of meat' is the wordplay.
'rotten' becomes 'off' (rotten food is 'off').
'bit of meat' becomes 'cut' (cut of meat).
'off'+'cut'='OFFCUT'
(Other definitions for offcut that I've seen before include "End" , "Small bit of some material" , "Remnant for other uses" , "Remnant of material" , "waste material" .)