You are a cone. You can see a picture of a cone and lots more information at http://en.wikipedia.org/wiki/Cone_(geometry)
A Cone.
A point
If your asking "What is ...?" Then, the answer is a circle. This is the definition of a circle!
Circle
It could be a circle or a sphere
A Cone.
A point
The center of a circle is an example of a point equidistant from all points on the circle's circumference, serving as the geometric midpoint of the shape. It is a key element for defining the circle's properties and relationships with other geometric figures.
All points equidistant from a center point.
tangent
If your asking "What is ...?" Then, the answer is a circle. This is the definition of a circle!
tangent
How about the circumference of a circle generated by a compass.
circle
Circle
It could be a circle or a sphere
The point in a circle from which all other points are equidistant is called the center. The distance from the center to any point on the circle is known as the radius. This property defines the geometric nature of a circle in Euclidean space.