Circle Geometry Terms

Diameter (d)

• A chord that passes through the center of the circle.

• A line segment connecting two points on the circle's circumference.

• The distance around the circle.

• A line segment that touches the circle at one point.

Chord

• A line segment that lies inside the circle with endpoints on the circle.

• A line that touches the circle at exactly one point.

• A line segment that connects two points on the circumference of the circle.

• A line that passes through the center of the circle.

Semicircle

• An arc that is half a circle.

• A full circle.

• A line segment connecting two points on a circle.

• A triangle inscribed in a circle.

Radius (r)

• A line segment with endpoints at the center and a point on the circle.

• A line segment connecting two points on the circle.

• The distance from the center of the circle to the circumference.

• A line that passes through the center of the circle and touches the circumference.

Center

• The point from which all points on a circle are equidistant.

• The outer boundary of a circle.

• The diameter of a circle.

• The area enclosed by a circle.

Central Angle

• An angle with vertex at the center and sides that are radii.

• An angle formed by two tangents to a circle.

• An angle whose vertex is on the circumference of a circle.

• An angle that measures more than 180 degrees.

Circle

• A polygon with three sides.

• All the points on a plane that are equidistant from a given point (the center).

• A closed figure with four equal sides.

• A straight line that connects two points.

Major Arc

• An arc that is less than half a circle (< 180°).

• An arc that is exactly half a circle (180°).

• An arc that is more than half a circle (> 180°).

• An arc that is a full circle (360°).

Arc

• A straight line connecting two points on a circle.

• A portion of a circle that connects two points along the ring of the circle.

• The area enclosed by a circle.

• A line segment that passes through the center of a circle.

Minor Arc

• An arc that is less than half a circle (< 180°). Typically written with two letters (e.g., AB).

• An arc that is exactly half a circle (180°).

• An arc that is greater than half a circle (> 180°).

• An arc that is a full circle (360°).