Reply coupons belong to postage stamps according to postal definition. These coupons are paying return postage for a standard international letter. The sender of a letter attaches a reply coupon to pay the return postage of the addressee. The addressee hands in the reply coupon at his or her post office and receives stamps for a standard international letter. Special services like airmail or registration may be paid for by using more reply coupons. There are two types of reply coupons, regional ones and international ones.