quadrant. 1 In analytic geometry, one of the four regions of the plane determined by two lines, the x-axis and the y-axis. Commonly these lines are drawn perpendicular to each other, and the quadrants, or regions, they determine are numbered counterclockwise, beginning with the upper right quadrant. 2 In geometry, a region of a plane determined by two perpendicular radii of a circle and the circle itself. Thus two perpendicular diameters of a circle divide it into four regions, or quadrants.

quadrant, in technology, angle-measuring device based on a scale of 90°. It is sometimes confused with the sextant, a similar instrument based on a scale of 60°. The quadrant is rarely used today.

Quadrant may refer to:

• One of the four sections of the Cartesian coordinate system
• Quadrant (instrument), a measuring instrument capable of measuring angles up to 90°
• In science-fiction: Galactic quadrants (Star Trek)
• HMS Quadrant (G11), a Second World War British/Australian warship
• A Quadrant or section in a city street nomenclature system
• Quadrant (automobile)
• Quadrant (magazine), an Australian journal
• Quadrant Shopping Centre, Swansea, Wales
• First Quebec Conference (1943) (codenamed "QUADRANT")
• A sector equal to one quarter of a circle, or half a semicircle
• Quadrant (architecture) a building which arcs in 90 degree manner