The first radio announcement of Japan's surrender by Emperor Hirohito was called Gyokuon-hōsō.
The Japanese term means the “Jewel Voice Broadcast.” It refers specifically to Hirohito's recorded speech, broadcast at noon on August 15, 1945. The recording had been made the previous day after Japan's leaders accepted the Allied surrender terms.
Hirohito spoke in formal classical Japanese, a style that many listeners found unfamiliar. The speech did not plainly say “Japan surrenders”; instead, it announced acceptance of the Potsdam Declaration and referred to the changing military situation and the destructive power of the atomic bomb. The broadcast was historically unusual because the emperor had rarely, if ever, been heard directly by the general public.
Gyokuon-hōsō is not the name of the surrender document. The printed legal document signed aboard USS Missouri was the Japanese Instrument of Surrender. Nor is the broadcast the same event as the September ceremony: it announced the decision, while the ceremony formalized it.