A First Day of Issue Cover or First Day Cover is a postage stamp on a cover, postal card or stamped envelope franked on the first day the issue is authorized for use within the country or territory of the stamp-issuing authority. Sometimes the issue is made from a temporary or permanent foreign or overseas office. There will usually be a first day of issue postmark, frequently a pictorial cancellation, indicating the city and date where the item was first issued, and "first day of issue" is often used to refer to this postmark. Depending on the policy of the nation issuing the stamp, official first day postmarks may sometimes be applied to covers weeks or months after the date indicated.
Postal authorities may hold a first day ceremony to generate publicity for the new issue, with postal officials revealing the stamp, and with connected persons in attendance, such as descendants of the person being honored by the stamp. The ceremony may also be held in a location that has a special connection with the stamp's subject, such as the birthplace of a social movement, or at a stamp show.
Various companies and individuals create these First Day Covers - from large companies that do hundreds a year, to small companies that do just a handful a year. (An individual can be just one person with a printer and a gift for design!)
Although the illustration on this FDC is of a WASP, the "first day ceremony" was actually for the Purple Heart stamp - something that a WASP was never awarded, since they were civilians and the Purple Heart is only for military personnel).