Definitions of sector:

• noun:   measuring instrument consisting of two graduated arms hinged at one end
• noun:   a particular aspect of life or activity

  Example: "He was helpless in an important sector of his life"

• noun:   a body of people who form part of society or economy

  Example: "The public sector"

• noun:   a portion of a military position
• noun:   the minimum track length that can be assigned to store information; unless otherwise specified a sector of data consists of 512 bytes
• noun:   a plane figure bounded by two radii and the included arc of a circle