A coupon is a voucher entitling the holder to a discount for a particular product, or it can be a form in a newspaper or magazine that may be filled in and sent as an application for a purchase or information.
People will never tire of saving money, and brands are always looking to bring in new customers. Mix in a decade-long struggling economy, and you have a savings-savvy mindset that isn't going away anytime soon.
One time I used a coupon when I went shopping. The coupon was for 25% off the price I would have originally paid.
Ebates, Coupons.com, and Groupon are all reliable websites to find coupons on.