inverted airplane airmail stampInverted airplane airmail stamp, U.S., 1918.
philately , Collection and study of postage stamps. The first postage stamps were issued in England in 1840, and in the U.S. in 1842. Stamp collectors usually specialize, collecting stamps of one country, one period of time, or one subject (e.g., birds, flowers, art). Value depends on rarity and condition. An issue of stamps that includes a printer’s error may have increased value.