« A planet is a celestial body that is in orbit around the Sun, which has sufficient mass for its gravity to overcome the cohesive forces of the solid body and maintain hydrostatic equilibrium (spherical), which eliminated all body moving on an orbit close ».
This definition was approved August 24, 2006, at the 26th General Assembly of the IAU by a vote to freehand, by 400 scientists after ten days of discussions.
If we could look at the solar system from outside, far above the Earth's north pole, we would see the planets orbit the Sun in the opposite direction of clockwise.
We find that the disk rotation of the planets is remarkably plan, only Mercury has an inclined relative to other (7°) orbit.
But we do not notice the planets rotate on themselves. Each planets revolve around a different axis of rotation.
The axis tilt or obliquity is the angle between the axis of rotation of a planet and the perpendicular to the orbital plane.