An interest payment (coupon) that covers a longer period than the other coupons on a bond. For example, in a semi-annual bond, the first interest payment might cover a period longer than the regular six months (say, nine months or a year). Long coupons are usually associated with the first interest installment.
Long coupon could also be another term for long bond, i.e., a bond with a long time until maturity date. Bonds with more than two years to maturity are often referred to as long coupon.
