is typically more expensive and has special postage rates. Commemorative stamps – stamps to commemorate events, anniversaries, etc., on sale for a limited time. Definitive stamps – the most common type of stamps Postage due stamps are special stamps applied by a post office to mail bearing insufficient postage. The stamps were issued in several denominations to make up different amounts due. Topical stamp collecting – many collectors choose to organize their philatelic collection on the theme of the stamps, covers, or postmarks. Popular topical themes are animals, dogs, cats, butterflies, birds, flowers, art, sports, Olympics, maps, Disney, scouting, space, ships, Americana (topics relating to the US), stamps on stamps, famous people, chess, Chinese new year, and many others. Birds on stamps Ships on stamps Insects on stamps People on stamps Stamps on stamps Postal stationery – includes government-issued postal cards, aerograms, letter card, wrappers, envelopes, etc., that usually have an imprinted stamp. Sheets Sheetlets – this is a format that is now issued regularly by postal administrations. Instead of issuing stamps in large sheets of 40, 100 or even 200 stamps, smaller sheetlets with 20 to 24 stamps are issued with a large selvedge area which may incorporate part of the stamp design or theme. Souvenir sheets – many postal services sometimes release stamps in a format that look like a sheet with a big picture. Various parts of the picture can be torn out and used as postage stamps. See example with 10 stamps in one picture. (Souvenir sheets should be distinguished from souvenir cards, which are souvenirs of a philatelic meeting or exhibition but are not valid for postage.) Miniature sheet – is very similar to a souvenir sheet, being in a sheetlet with a single or a number of stamps embedded in it. Corner blocks or plate blocks – compose a block of stamps from one of the four corners of the stamp sheet. Collectors usually opt for a block of four stamps, complete with the selvage area which will sometimes have the printing details on it. Coil strips – Pairs or more of stamps from rolls, premium ones showing the plate number or a coil line pair which shows the seam between the edges of the plate. Revenue stamps – stamps issued to pay taxes. Federal Duck Stamps (stamps for duck hunting licenses, mainly U.S. with some other countries such as Canada and New Zealand)