In Euclidean geometry, an arc (symbol: ⌒) is a closed segment of a differentiable curve.
Area is the quantity that expresses the extent of a two-dimensional figure or shape, or planar lamina, in the plane.
Central angles are subtended by an arc between those two points, and the arc length is the central angle of a circle of radius one (measured in radians).
In geometry, a circular segment (symbol: ⌓) is a region of a circle which is "cut off" from the rest of the circle by a secant or a chord.
In mathematics, a conic section (or simply conic) is a curve obtained as the intersection of the surface of a cone with a plane.
A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360 degrees.
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle.
In geometry, a disk (also spelled disc).
A perimeter is a path that surrounds a two-dimensional shape.
The radian (SI symbol rad) is the SI unit for measuring angles, and is the standard unit of angular measure used in many areas of mathematics.
In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length.
In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle.