Alternatively referred to as a promo code, a coupon code is a special series of characters used on e-commerce websites to get a discounted price or limited offer on an order. Coupon codes can be obtained from advertisements, reaching a specific dollar amount with all purchases made, or as an incentive for being referred by an existing customer.
Depending on the website, coupon codes can be used when purchasing a product in the online shopping cart or the URL of the website (example.com/couponcode).
A popular site that provides coupon codes for many online retailers is RetailMeNot (https://www.retailmenot.com). It provides an interface for users to search for retailers, display coupon codes that may or may not be currently valid, and see how many other users have successfully used that code.