A promo code is typically a short, alphanumeric code entered during checkout to receive a discount or promotion. A voucher, on the other hand, usually refers to a document-digital or physical-that holds a set value or specific reward, like a $10 gift voucher. Vouchers can sometimes be used like cash, while promo codes often apply specific terms, such as a percentage off a certain product. Vouchers may also have more formal issuance and redemption rules than promo codes.