A commemorative stamp is a special type of postage stamp that is created to honor an important person, event, or significant anniversary. It is like a small piece of art that is used to celebrate or remember something special. Full definition
The United States Postal Service issued a 44 - cent Abstract Expressionists commemorative stamp in ten designs. (arshilegorkyfoundation.org)
The envelope had the words «Grandmasters Invitation» and stamps from the Republic era on the front and on the back was The Grandmasters limited edition commemorative stamp with postmarks from Kowloon Hong Kong, Foshan Guangdong, Peking, Fengtian and other locations. (wongkarwai.net)
Similarly, US and foreign commemorative stamps and first day covers make great prizes. (organicmania.com)