八折 or 八折优惠，1 折=10%，八折 means the good price is reduced to be 80% of the original

八折

打 八折 (v.) (The price*80%) For example: Excuse me, do you offer any discount now? (請問現在有打折嗎?) Yes, we save up to 20% off on all polo shirts, except Tommy Hilfiger. (是的，全部的Polo衫打八折，除了Tommy Hilfiger) P.S. This is the reason why I simultaneously love and hate Tommy Hilfiger.

20%off =打＂八折＂

Even when I, a Chinese, first heard "八折", I thought that they reduced the price by 80%.