## What is a circumference?

Formally, a circumference is defined as the locus of points from the plane equidistant to another point, called the center of the circumference.

We must never confuse the concept of a circle with the concept of circumference, circumference is actually a curve that encloses a circle (the circumference is a curve, the circle is an area.)

Here we see an image of a circumferece.

Actually, more simply, a **circle is the set of points in the plane that are all at the same distance from one central point**, which we will call the center.

## Basic elements

In the image above you can see all the elements that we are going to introduce:

**Center**: center point that is equidistant to all points belonging to the circumference.**Radius**: line connecting the center with any point belonging to the circumference.**String**: line connecting any two points of the circumference.**Diameter**: longer line connecting two points of the circumference. There are infinite diameters and all pass through the center of the circumference.**Secant line**: line that cuts through any two points of the circumference.**Tangent**: line touching the circle at just one point and perpendicular to a radius.