A sector is a part of a whole. As a well the specific usages below, it can also be used metaphorically, referring to a generic piece or portion of something.

• Sector is an unincoporated community in West Virginia, in the United States.
• sector can refer to a geographic subdivision, zone, region, area, especially one that is assigned to a military control. For example, Allied Occupation Zones in Germany.
• In Euclidean plane geometry, a sector is a "pie-shaped" part of a disk enclosed by two radii and an arc. In the special case of the circle being divided into 2 equal sectors, they are called halves; divided into 4 equal sectors, they are called quadrants; divided into 8 equal sectors, they are called octants.
• In the context of computer hardware, a sector is a sub-division of a track of a magnetic hard disk or optical disc. A sector stores a fixed amount of data. The typical formatting of sectors allows holding 512 bytes (e.g. harddisks and diskettes) or 2048 bytes (e.g. optical discs) of data. (See also Cylinder-head-sector, hard disk drive partitioning, FAT.)
• In economics, economic activity is often categorised into sectors, in a variety of schemes. For example private sector vs public sector; service sector vs manufacturing sector; primary sector/ secondary sector/ tertiary sector.
• In Formula 1, a sector is a section of the track defined for timing purposes. There are usually 2 or 3 sectors on a track.
• In a mobile phone network, a sector is a small part of the network's radio coverage area, served by a set of antennas and equipment at a cell site.
• A Sector is a mathematical instrument consisting of two hinged arms with various scales

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