Definition of a planet: "A planet is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (spherical) shape, and has cleared the neighborhood around its orbit."
This definition was approved on August 24, 2006, during the 26th General Assembly of the IAU by a show of hands of 400 scientists after ten days of discussions.
If we could observe the Solar System from the outside, far above the Earth's North Pole, we would see the planets orbiting the Sun in a counterclockwise direction.
We would notice that the plane of the planets' rotation is remarkably flat; only Mercury has an orbit inclined relative to the others (7°).
There are articles on this page
Perihelion and Aphelion: The Apsides in the Solar System 
Winds of the solar system and giant planets
3D Simulator: Revolutions of the Planets
Planet Mercury
Venus, the Shepherd's Star
Earth, the Blue Planet: A Fragile Jewel in the Universe
Mars: The Conquests and First Human Steps on the Red Planet
Planet Jupiter
Saturn: The Ringed Giant of Ice and Rock
Planet Uranus
Neptune: The Blue Giant of the Solar System
Roche limit
Remarkable characteristics of the planet Venus
Remarkable characteristics of the planet Jupiter
Remarkable characteristics of the planet Saturn
Characteristics of Planets: What Makes Them Unique
Venus, Veiled Planet: A Puzzle in our Solar System
Live on Mars
The seven wonders of the World
Planet 9 is still nowhere in sight
Axial Tilt of Planets: An Unstable Dance Through the Ages
Comparative sizes of planets and stars
The Journey of the Planets Along the Ecliptic: A Cosmic Choreography
Declination and right ascension
Saturn's Rings: A Ring System in Jeopardy