The eccentricity of a circle is zero. For a curved shape such as an ellipse, parabola or hyperbola, the eccentricity indicates how far away the shape is from being a circle. The more circular the shape is, the smaller the eccentricity. However, the flatter it is, the greater the eccentricity.
The eccentricities of certain shapes fall within defined ranges. For an ellipse, the eccentricity lies between zero and one. A parabola, which is typically more stretched out, has an eccentricity of one. The eccentricity of a hyperbola is greater than one. However, a straight line has an eccentricity of infinity. In a practical application, the eccentricity of the earth's orbit around the sun is 0.02, because the path is not quite circular.