Definition of Circle
This section of about the definition of a circle. A circle is often used in geometry and knowing the definition of a circle is the first step towards calculating the area of a circle or the circumference of a circle.
What is the definition of a circle?
The definition of a circle is as follows: A circle is the set of all points in a plane having the same distance from a fixed point.
Center of the circle or origin
The fixed point in the middle of a circle is called the center of the circle or the origin. In the circle on the right, the origin is marked 'O'. 

Definition of a radius
The distance between the center of the circle and any point of the circle is called the radius of the circle. Radii is the plural for radius. OB is the radius of the circle above as is OA.
Definition of a chord of a circle
The chord of a circle is a line segment whose end points lie on the circle. In the circle above, PQ is a chord of the circle.
Definition of the diameter of a circle
The diameter of a circle is a chord that passes through the center of the circle. Here AB is the diameter of the circle.
Definition of the arc of a circle
An arc of a circle is a curved, such as QB, portion of a circle.
