Coupon
Also called: Promo code, Discount code, Voucher
A code that gives a discount or free shipping, usually with rules like expiry and minimum order.
Definition
Coupon logic is full of rules: minimum order value, expiry dates, one use per customer, which products qualify and whether codes can be combined. That makes it a favorite place for testers to look for money-losing bugs.
In practice
Applying SAVE10 twice should not give 20% off, and an expired code should show a clear message.