The discount code system allows website owners to setup vouchers within their website. These vouchers can be promoted and given out to potential customers allowing discounts from products on the site.
The discount can be time limited, percent or fixed price discounts, discounts off certain departments or products and limited in use (for example limited to one per customer).
This feature works well as part of a viral marketing strategy as people on the Internet tend to share vouchers and discount codes to their friends and family.