A segment that joins the center of a circle to any point on the circle is called a radius.

Key Points about the Radius:

1. The radius is constant for all points on the circle.
2. The length of the radius is half the diameter of the circle.
3. It is a crucial part of the formula for calculating the area ($A = \pi r^2$) and circumference ($C = 2\pi r$) of the circle.

Would you like me to elaborate on its applications or properties?

Here are 5 related questions you might find interesting:

1. What is the relationship between the radius and diameter of a circle?
2. How do you calculate the area of a circle using the radius?
3. How is the radius used in finding the equation of a circle in coordinate geometry?
4. What is the difference between the radius and a chord in a circle?
5. How do you determine the radius of a circle if the circumference is given?

Tip: Always label the radius clearly in a diagram of a circle