The promotion code represents a coupon or discount that can be applied to your total cost. These promotions vary with travel dates, airlines and locations. If you have a promotion code you would like to use, enter the code into the blank and click the "update" button. You should now see your discount listed in the pricing section.
NOT COMBINABLE: No two promo codes or "automatic" discounts (limited-time specials) you may already see in the pricing box can be combinable. When you click update, the last valid discount is the one which will be used.