Final answer:
The paper of a self-adhesive postage stamp is referred to as 'stock' and the sticky material on the back of the stamp is called 'adhesive'.
Step-by-step explanation:
Postage stamps are now self-adhesive. The paper is referred to as 'stock' and the sticky material on the back is termed the 'adhesive'. Stamps have evolved over time, and modern postage stamps no longer require the use of separate glue or moisture to adhere to an envelope. Instead, the self-adhesive stamps come with a sticky backing covered by a release paper or release coating. The front side of a stamp, which has the design, is printed on the stock, while the rear side is coated with an adhesive that allows for easy application.