This is a First Day of Issue from 1982. A first day cover (FDC) is an envelope where the postage stamps have been canceled on their first day of issue. 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. [Wikipedia]
I have included it on this site because the design is exquisite and the craftsmanship is superb. The illustration really captures the look of a library, pre-computer era. Also noteworthy, is the wording on the 20 cent stamp: "America's Libraries: Legacies to Mankind" Technically, this area of postal history may be considered "philately" or the study of stamps.