Consider this example: you offer a 10% discount to active duty military at your business. When someone comes in and presents their military ID, you take 10% off their bill. That’s a discount for a specific circumstance. Swap out military for cash, and you have yourself a cash discount. Surcharging would be where you offer a 10% active duty military discount, but instead of discounting the total for those who can prove their status, you charge an extra 10% to those who can’t prove status. One is a fee added to the total and one is a discount off the total.