A circle is the set of all points that have the same distance from another point (the center of the circle). This distance is called radius.

## Parts of a circle

In the following we name the different parts of a circle. Consider the following image:

- Center
- the center point of the circle.
- Radius
- any line going from the center point to any point on the circle.
- Diameter
- a line going from one point on the circle to another point on the circle passing through the center point (the length is twice that of the radius).
- Chord
- a line going from one point on the circle to another point (the diameter is also a chord).
- Secant
- any line that contains a chord.
- Tangent
- a line touching the circle in one point.
- Point of tangency
- the point where the tangent is touching the circle.