SP505, U.S. #1846, Henry Clay Regular Stamp USPS Souvenir Page. First Day of Issue July 13, 1983, Washington DC 20066. Scan is an example. Never folded, shipped flat in a sheet protector.
USPS Souvenir Pages or American Commemorative Cancellations are -Official First Day of Issue Cancellations, which are a mint stamp or stamps affixed to an 8"x10.5" color page, and include technical and historical information about the stamp or stamps and the designer. The pages were issued flat and unfolded.