In mathematics, the radius is the distance from the center of a circle or sphere to any point on its circumference or surface, respectively.

Here's a breakdown:

* Circle: The radius of a circle is the length of a line segment drawn from the center of the circle to a point on its circumference.

* Sphere: The radius of a sphere is the length of a line segment drawn from the center of the sphere to a point on its surface.

Key Points:

* The radius is always a positive number.

* The radius is half the diameter of the circle or sphere.

* The radius is used in various formulas related to circles and spheres, such as calculating circumference, area, and volume.

Let me know if you'd like to explore any specific applications of radius in mathematics!