Ho trovato queste definizioni:
"An overrider is a retrospective discount agreement commonly sought by major supermarkets and other retail multiples for target achievement: typically values range between 0.5% and 4%. Overrider discounts are normally paid in addition to listing fees (the sums of money suppliers pay retailers to list new lines or just to retain existing listings), promotional costs and advertising rebates. The overrider discount is not deducted from invoice; it is made as a separate payment

Http://wiki.keystonesupport.net/wiki_kcx/index.php?title=Customer_Discountshttp://www.kamcity.com/kamwords/worddesc.asp?WordID=3040

"un tipo di sconto che il fornitore / venditore dà sul prezzo già concordato"
http://www.proz.com/kudoz/english_to_portuguese/business_com...