Concession (3)
'concession' is the definition.
(I know that sop is a type of concession)
This is all the clue.
(Other definitions for sop that I've seen before include "Propitiatory gift" , "Concession given to mollify or placate" , "Appeasing gift" , "Piece of bread dipped in liquid, or a concession" , "Propitiatory offering" .)
(Other definitions for trade-off that I've seen before include "Exchange that occurs as a compromise" , "Exchange that is part of a compromise" .)