What is a circle and what makes a circle defined

Step-by-step explanation:

A circle is a geometric figure made up of a bunch of points that are all equidistant from a center.  For example, you might choose a central point and then mark a dozen or so points that are 3 inches from that center.  That would be a circle of radius 3.

The simplest equation of a circle is

x^2 + y^2 = r^2, where r is the radius of the circle and the center is at the origin (0, 0).

For a circle whose center is not at the origin (not at (0, 0) ), the general equation of a circle with center at (h, k) is

(x-h)^2 + (y-k)^2 = r^2

A circle is a set of points in a plane that are a given distance from a given point in the plane.

The given point is called the center of the circle and the given distance from any point on the circle to the center is called the radius. It does not matter what point on the circle you choose because they are all the same length from the outside of the circle to the center. So, we can say that all radii of a given circle are congruent.