A First Day Cover is a specially designed cover issued at the same time as a new stamp and thematically related to the issue. It is generally abbreviated FDC, from the English expression First Day Cover ; catalogues also use this abbreviation. An FDC makes the release of a new stamp more ceremonial. The stamp affixed to the illustrated cover attracts even greater attention and highlights the beauty of the issue.

Hungary’s first FDC was issued in 1947 for the Aircraft IV series. At first, only the cancellation indicated its first-day character: the new stamps were affixed to ordinary envelopes and then cancelled with a first-day postmark.

Later, demand developed for illustrated covers more closely associated with the release of a new stamp or souvenir sheet. The design of an FDC is usually closely connected with the subject of the stamp issue, and in many cases the same artist designs both. A special commemorative postmark related to the theme is also often created for the FDC.

Like souvenir sheets, FDCs are produced primarily for collectors. They have only rarely passed through the postal system in genuine commercial use. Covers that were actually mailed on the day of issue are usually more valuable.