# Definition and basic elements of a circumference

## 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.