This is Ryukyu islands postage stamps. The current Okinawa Prefecture, which was ruled by the US military for about 20 years from the end of World War II until its revision to Japan in 1972, was indirectly governed as an upper organization under the name of the Ryukyu government. This postage stamp is called “Ryukyu stamp” because it was issued during that period. Since Ryukyu is a general term for many islands, the islands are collectively described as “Ryukyus” in the stamps.