How to Identify Radii, Chords, and Diameters
When you work with circles, there are three straightline components that you need to be able to identify: radii, chords, and diameters.

Radius: A circle’s radius — the distance from its center to a point on the circle — tells you the circle’s size. In addition to being a measure of distance, a radius is also a segment that goes from a circle’s center to a point on the circle.

Chord: A segment that connects two points on a circle is called a chord.

Diameter: A chord that passes through a circle’s center is a diameter of the circle. A circle’s diameter is twice as long as its radius.
The above figure shows circle O.