There are mainly 4 categories of stamps in Singapore:
1. Definitive stamps. These are stamps printed to meet Singapore's normal postal demand. New definitive stamps are usually released every 3 to 5 years.
2. Commemorative Stamps. These are stamps that celebrate significant national and international events like YOG, APEC 2009, etc.
3. Special stamps. These stamps depict subjects of general interest such as flora, fauna, culture, history and architecture.
4. Greetings Stamps. These stamps can be used on special occasions to convey joyous messages. An example will be Christmas stamps or Chinese New Year stamps.