A selection of Hong Kong postage stamps A postage stamp is an adhesive paper evidence of pre-paying a fee for postal services. Usually a small paper rectangle or square that is attached to an envelope, the postage stamp signifies that the person sending the letter or package may have either fully, or perhaps partly, pre-paid for delivery. Postage stamps are the most popular way of paying for retail mail; alternatives include prepaid-postage envelopes and postage meters.