ˈsɛk.təɹ sfɪə sfɪɹ measuring instrument consisting of two graduated arms hinged at one end a particular aspect of life or activity he was helpless in an important sector of his life a social group that forms part of the society or the economy the public sector a portion of a military position the minimum track length that can be assigned to store information; unless otherwise specified a sector of data consists of 512 bytes a plane figure bounded by two radii and the included arc of a circle