What is the meaning of sector?

noun

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