| A | B |
|---|
| Circle | The set of all points equidistant from a given point |
| interior point | A point inside the circle |
| exterior point | A point outside the circle |
| Chord | A line segment whose endpoints lie on the circle |
| Diameter | A chord that passes through the center of a circle |
| Radius | A line segment that has one endpoint at the center of the circle and the other endpoint on the circle |
| Tangent | A line that intersects a circle in one and only one point |
| Point of tangency | The point where a line touches a circle at one point only |
| Secant | A line that intersects the circle in two points |
| Common internal tangent | A line that is tangent to two circles and crosses a line segement that connect the centers of the two circles |
| Common tangent | A line that is tangent to two circles that are also tangent to each other |
| Common external tangent | A line that is tangent to two circles but does not intersect a line segment that connects the centers of the two circles |
| Concentric circles | Circles with the same center |
| Central angle | An angle whose vertex lies at the center of the circle |
| Arc | An unbroken part of a circle |
| Minor Arc | An arc whose measure is greater than zero degrees but less that 180 degrees |
| Major arc | An arc whose measure is greater than 180 degrees but less than 360 degrees |
| Semicircle | An arc whose measure is exactly 180 degrees |
| Inscribed angle | An angle whose vertex lies on the circle |
| Sector | An area of a circle created by two radii |
| Intercepted Arc | An arc lies on the circle within the two sides of an angle. |
