# What is the radius?

Most often, the term "radius" is used in geometry. It was first used by the French scientist P. Ramus as early as 1569, although the term became common only at the end of the 17th century. Literally from the Latin radius is translated as "beam, spoke wheel."

Let's take a closer look at what radius is in geometry.

## Radius is ...

Radius is a segment that connects the center of a circle or sphere with any point on the circle or sphere. The length of this segment is also called the radius. Note also that the radius is equal to half the diameter.

If you need to find the radius of the circumscribed circle, then you can use the formulas from the article How to find the radius of the circumscribed circle.

As for the radius of the inscribed circle, then the algorithm for its calculation can be found in the article of our website How to find the radius of the inscribed circle.

The term "radius" is another meaning when we speak of a radius vector. The radius vector is a vector that defines the position of a point in space relative to some pre-fixed point. This point is called the "origin".

The term "radius" can be used not only in a scientific context, in particular, experienced drivers can talk about the turning radius. In this case, the turning radius is the radius of the circle described by the external (maximum distance from the center) point of the car.