An interest payment on a bond that is more or less than interest payment of typical six months. This is the case with the first coupon payment on many bonds because payment period is different from standard six months from the date of issuance. When the first coupon payment is less than six months, the bond is said to have a short first coupon. The first coupon payment could also be received in less than six months when a bond is purchased between coupon dates.
An irregular coupon is also known as an odd coupon.
