Referral / Promo Code
What is Referral
It is a code/card issued by a business owner to his promoters, to increase his sales by using the promoter's contacts sphere.
Here, the promotor will get an incentive, once he recommends the business to his network.
First, the business owner needs to issue a referral/promo code to the promotor, and then he can give that code to his friend or someone.
When the person, who has the referral code, buys goods from your business, you can issue an incentive to the promotor too, while giving a discount to the customer.
This can call as "Word of Mouth Sales"