What is a commemorative stamp?

Answer 1

A commemorative stamp is issued to commemorate a special event or historic milestone. The US issues such items to mark anniversaries, such as statehood, founding of organizations, and other culturally significant items. They are usually available for a short period of time, typically several months and are printed in limited quantities.

Answer 2

About commemorative postmark definitions , various philatelic dictionary claims the same , but the effect can be summarized as follows: " postal department to commemorate a major festivals , major events or stamp issue with a commemorative engraving text or pattern the postmark. limited datestamped postage certificate, have the the postage datestamped function.