What is the difference between eccentricity, obliquity, and precession?
Eccentricity is a characteristic of Earth's orbit around the Sun. Obliquity is angle between Earth's spin axis and the normal to ecliptic. Precession is periodic perturbation to the spin axis..
The orbit of the Earth is an ellipse with the Sun at a focus. The eccentricity of this ellipse e = 0.0167, nearly.
Obliquity is the inclination
This polar axis turns around its mean position completely once in a great Year period of about 25800 years. This motion is called the Earth's axial precession.