Editing Definitive stamp (section)

== Collecting ==
Since definitive series are issued over a period of time and are reprinted to meet postal demand, they often contain more variation than is typically found in stamps that have a single print run. Switching printing methods and experimenting with phosphors is a common source of variation in modern stamps, while differences in watermarks and perforation are also prevalent, especially in older stamps. Many philatelists study these differences as part of their hobby and try to collect all the varieties of each stamp. Some varieties are particularly rare and can be more valuable than others of the same stamp that may look the same to the casual observer.  One notable example of this variation is the [[List of Machin stamps|Machin stamps]] of the UK, where philatelists have identified over 1,000 varieties of the same basic design.

[[Special stamp]]s, such as the [[Christmas stamp]]s issued annually by various countries, are sometimes regarded as definitives because they are not commemoratives, but they typically only include a limited range of denominations relating specifically to the mail seen on the occasion for which they are issued.