Mail-use stamps are the most common. Usually less than an inch square, they’re printed in large quantities and often more than once.
Commemorative stamps honor people, events, and subjects of importance to American life and culture. They are printed in smaller quantities as part of an annual program and usually only once. Larger than mail-use stamps, many commemoratives are printed in “semi-jumbo” size, the largest standard size in use.
Special stamps — such as stamps for holiday celebrations and the Love series stamps — are larger and typically on sale for a limited time.
Semipostal stamps are a type of special stamp sold at a price above the First-Class™ rate, with the overage going to support a particular cause, such as breast cancer research.
Stamps can be “denominated” with a specific numeric rate (e.g., two cents) or “nondenominated.” The latter will always be valid for the current applicable rate. First-class, one-ounce, “nondenominated” stamps are commonly known as Forever® stamps. The majority of stamps issued in recent years fall into this category.
Some stamps, especially older issuances, have water-activated adhesive (“lick-and-stick”) and may require careful storage to avoid having the adhesive adhere to an album page or to other stamps. Today’s stamps are typically issued as self-adhesive or pressure-sensitive (“peel-and-stick”).
