Coupon's are simply explained, they are a way of saving money, company's (both online and high street/brand) often issue coupons that you present in order to save money on specific purchases (just like the 50 pence off' coupon on your cereal box) , this applies to some of the popular online DVD retailers who have been known to offer promotional coupons for money off there purchases. A good resource for fingig more about coupons might be http://www.dvdtalk.com.