A circle is defined as the set of all points in a plane that are equidistant from a center point. The radius is the distance from the center to any point on the edge, while the diameter connects two points on the edge through the center and is twice as long as the radius. The circumference is the distance around the edge of the circle. Other terms include chord (a line connecting two edge points not through the center), arc (a curved section of the edge), segment (region between a chord and arc), sector (wedge-shaped area between radii and an arc). The area of a circle is calculated as π times the radius squared.

1. Circle

2. Circle
 The set of all points on a plane that are a fixed
distance from a center.
 A circle is a simple shape of consisting of
those points in a plane that are equidistant from a
given point, the centre.

3. Circle illustration showing a radius, a diameter,
the centre and circumference

4. Radius
 The distance between any of the points and the
centre is called the radius.
 The Radius is the distance from the center to the
edge.

5. Diameter
 The diameter is a line segment that connects two
points on the circle and goes through the centre
of the circle. It is always twice as long as the
radius.
 The Diameter starts at one side of the circle,
goes through the center and ends on the other
side.

6. Circumference
 The Circumference is the distance around the
edge of the circle.

7. Radius, Diameter and Circumference

8. Chord, Arc, Centre and Diameter

9. Chord
 A chord is a line segment whose endpoints are at
any two points on the circle and it doesn’t pass
through the centre

10. Arc
 An arc of a Circle is a curved line drawn between
two points along the circumference of a Circle.

11. Segement
 A segment is a region bounded by a chord and an
arc lying between the chord’s endpoints.

12. Circumference
 A semicircle is an arc that is defined by diametric
points along the circle. This arc is as large as half
(semi) the circle.
 Half a circle is called a Semicircle.
 C=2*Π*r

13. Sector
 Sector, is the portion of a disk enclosed by
two radii and an arc, where the smaller area is
known as the minor sector and the larger being
the major sector.

14. Segment and Sector
 The "pizza" slice is called a Sector.
 And the slice made by a chord is called
a Segment.

15. Area of a Circle
 The area of a circle is π times the radius squared,
which is written:
 A = π × r2