The fourth part; the quarter.
- Mathematics A circular arc of 90°; one fourth of the circumference of a circle.
- Mathematics The plane area bounded by such an arc and two perpendicular radii.
- Mathematics Any of the four areas into which a plane is divided by the reference axes in a Cartesian coordinate system, designated first, second, third, and fourth, counting counterclockwise from the area in which both coordinates are positive.
- A machine part or other mechanical device that is shaped like a quarter circle.
- An early instrument for measuring altitude of celestial bodies, consisting of a 90° graduated arc with a movable radius for measuring angles.