radius
A line segment with one endpoint at the center of a circle and the other endpoint on the circle
chord
line segment whose endpoints are any two points on a circle
circle
The set of all points in a plane that are the same distance from a given point called the center
diameter
a chord that contains the center of the circle
secant
a line that contains a chord
tangent
a line in the plane of a circle that intersects the circle in exactly one point
congruent circles
circles with congruent radii
concentric circles
circles that lie in the same plane and have the same center
inscribed polygon
A polygon whose vertices all lie on a circle.
circumscribed circle
The circle around a polygon where every vertex of the polygon lies on the circle