What was the official document signed aboard USS Missouri at Japan's surrender ceremony?

The official document signed aboard USS Missouri was the Japanese Instrument of Surrender.

Representatives of Japan and the Allied powers signed the instrument on September 2, 1945. General Douglas MacArthur signed first for the Allied powers, followed by Japanese representatives and delegates from the United States, China, the United Kingdom, the Soviet Union, Australia, Canada, France, the Netherlands, and New Zealand.

The document formally recorded Japan's unconditional surrender and required Japanese forces to cease hostilities and obey the orders of the Allied supreme commander. The ceremony therefore transformed the political announcement of surrender into a formal military act.

The Instrument of Surrender is distinct from the Potsdam Declaration. The declaration set out Allied demands in July 1945; Japan's acceptance of those terms was announced by Hirohito in August. The instrument was the document signed at the Tokyo Bay ceremony in September.