The circle is perhaps the purest, most profound and the most common symbol in existence. With the probably infinite billions of stars, planets, moons and galaxies full of the same, the circle is well represented in the physical universe in the form of spheres. A circle, having no beginning or end, represents infinity, eternity, wholeness and femininity. Other meaningfully significant symbols or objects are circular: Stonehenge, Ouroboros, the Wheel of Life, a halo around the head of a saint, etc. In a very practical way, it can be said that circles rule the world. For example: wheels, gears, computer hard drives, CDs.

The circle is such a common shape that we take it for granted ... but there is more to it that just a common shape. Mathematically, the circle is defined as the set of all points that are the same distance from a given point, called the center.
mathforum.org/~sanders/geometry/GP17Circle.html