Commemorative postage stamps often come in one of two formats, Mint or Cancelled to Order (CTO).
A mint stamp is one which is in its original state of issue, is unused, has never been mounted and has full gum. In practice, the term mint, is used within philately to refer to any stamp that appears to be unused, including those without gum, or previously hinged. Unlike other collectibles, a mint stamp may be in poor condition but still be regarded as being in mint state as long as it is apparently unused.
A cancelled to order postage stamp is a stamp the issuing postal service has cancelled (marked as used), but has not travelled through the post, but instead get handed back to a stamp collector or dealer. They can come from withdrawn stocks of stamps cancelled in sheets and sold as remainders or from new sheets for sale at reduced rates to the stamp trade. Postal services of various countries do this in response to collector demand, or to preclude stamps issued for the collector market being used on mail. Some of the history of CTOs is from stamps being given to collectors on an approval basis, in person or through mailings; the first CTOs began in the late 19th century.