| A | B |
|---|
| Circle | Set of points in a plane a given distance from a given point in the plane |
| chord | Segment whose endpoint lies on the circle |
| diameter | chord passing through the center of a circle |
| secant | line containing a chord |
| tangent | line in the plane of a circle that intersects the circle in exactly one point |
| point of tangency | point where the tangent intersects the circle |
| sphere | set of points in space a given distance from a given point |
| congruent circles (spheres) | circles (spheres) with congruent radii |
| concentric circles | circles in the same plane with the same center |
| inscribed angles | angle whose vertex is on a circle and whose sides contain chords of a circle |
| congruent arcs | arcs in the same circle, or congruent circles, that have equal measure |
| semicircle | arc whose endpoints are also the endpoints of a diameter |
| arc | unbroken part of a circle |
| central angle | angle with its vertex at the center of the circle |
| tangent circles | coplanar circles that are tangent to the same line at the same point |
| internal tangent | crosses the line of centers |
| external tangent | does not cross the line of centers |
| common tangent | line tangent to each of two coplanar circles |
| line of centers | line (ususally imaginary) joining the centers of two coplanar circles |
