The center of a circle is simply referred to as the center. However, it is often given the distinction of "0" in drawings and formulas of circles. The center of a circle is defined as the point from which all points of the circumference are equidistant.
The center of the circle is important because it is instrumental in figuring out other properties of the circle. For example, the radius of a circle can be found by measuring the distance from the center of the circle to the outer edge of the circle. The diameter equals the radius measurement times two.