Definitive Stamps
Like the United States "Forever" Liberty Bell stamp, definitive stamps can be used for postage all the time. Typically featuring flags and historic figures, definitive stamps are smaller and simpler than most other types of stamps, using only a few colors. The first definitive stamps in the United States were printed in 1847, and featured George Washington and Benjamin Franklin.
Commemorative Stamps
Larger in size and printed in smaller quantities than the definitive stamp, commemorative stamps recognize an important event or an organization, like the American Cancer Society. They are not reprinted after the original print run sells out. The first commemorative stamp printed in the United States was created to honor Columbus's discovery of the New World. Called the Columbian Exposition issue, the stamp first appeared in 1893.
Special Stamps
Stamps to celebrate holidays and other unique stamps, like the "Love" stamp series, are considered to be special stamps by collectors. Like definitive stamps, special stamps are often available for a long time and may be reprinted. However, like commemorative stamps, they're often larger than a definitive stamp.
Other Stamps
Although the first-class stamp can be used on almost anything, individual stamps can be purchased through the U.S. Postal Service for postcards, international and priority mailings. Additional postage stamps are also available to purchase through the U.S. Postal Service in a variety of nonstandard denominations.