From GroupScript documentation
Discount coupons can be given to users to offer a discount on site's offers.
Coupon code is the code you will give to your users (or use that in ads).
Discount type designates whether the coupon value will be in percent of order (i.e. if discount type is percent, and a value of 15, the user will receive a 15% discount on order if he types in the coupon code), or a fixed value (total), which will be deducted from order total.
Coupon type: permanent coupons can be used more than once, gift coupons can be used only once.