- chord: a line segment within a circle that touches 2 points on the circle.
- circumference: the distance around the circle.
- diameter: the longest distance from one end of a circle to the other.
- origin: the center of the circle
- pi (): A number, 3.141592…, equal to (the circumference) / (the diameter) of any circle.
- radius: distance from center of circle to any point on it.
- sector: is like a slice of pie (a circle wedge).
- tangent of circle: a line perpendicular to the radius that touches ONLY one point on the circle.
arc: a curved line that is part of the circumference of a circle