indian ocean islands British Indian Ocean Territory An overseas territory of the United Kingdom situated in the Indian Ocean, halfway between Africa and Indonesia. The territory comprises the six atolls of the Chagos Archipelago with over 1,000 individual islands. LanguaL curation note: US FDA 1995 Code: IO British Indian Ocean Territory An overseas territory of the United Kingdom situated in the Indian Ocean, halfway between Africa and Indonesia. The territory comprises the six atolls of the Chagos Archipelago with over 1,000 individual islands. LanguaL curation note: US FDA 1995 Code: IO