Center This point is exactly in the middle of the circle.
Radius A line from the center point to a point on the circle’s arc.
Cord A segment between two points on the circle. A cord does not have to go through the center point.
Diameter A segment between two points on a circle which goes through the center point. Can be abbreviated d.
Circle Arc A continuous length of a part of the circle’s circumference.
Circular segment An area which is limited by a circle’s arc and a cord between the arc’s endpoints.
Circle Sector An area which is which is limited by a circle’s arc and radiuses to the arcs end points.
The Circle’s Area and Circumference The Circle’s Area Can be defined as the measure of the surface within the circle’s arc. Area = p · r^{2} The Circle’s Circumference Can be defined as the measure of the circle’s arc. Circumference = p · 2r = p · d
Inscribed circle
Circumscribed circle