Circle
Set of all points in a plane that are equidistant from a given point
Center of Circle
The given point that is circle is equidistant from
Radius
Distance from the center to a point on a circle
Congruent Circles
Two circles that have the same radius
Diameter
The distance across the circle through the center
Chord
A segment whose endpoints are on the circle
Secant
A line that intersects a circle in two points
Tangent
A line in the plane of a circle that intersects the circle in exactly 1 point
Tangent Circles
Coplaner circles that intersect in one point
Concentric Circles
Coplaner circles with a common center
Common Tangent
A line or segment that is a tangent to two coplaner circles
Interior of a Circle
Points that are inside the circle
Exterior of a Circle
Points that are outside the circle
Point of Tangency
Point at which a tangent line intersects the circle to which it is tangent
Central Angle
An angle whose vertex is the center of a circle
Minor Arc
Arc on the interior of the central angle
Major Arc
Arc on the exterior of the central angle
Semicircle
formed if the endpoints of an arc are the endpoints of the diameter
Measure of a Minor Arc
Measure of its central angle
Measure of a Major Arc
The difference between 360 degrees and the measure of the minor arc
Congruent Arcs
Two arcs of the same circle (or of congruent circles) are congruent arcs if they have the same measure