Though the actual definition is somewhat rocky, a planet can be simply defined as a large celestial body with a spherical shape other than a star or satellite (i.e. moons).
Obviously, this tag only applies when the planet in question is observed from outside (or, in borderline cases, very near the edge of) the atmosphere.

Planets

• earth
• jupiter_(planet)
• mars_(planet)
• mercury_(planet)
• neptune_(planet)
• pluto_(dwarf_planet)
• saturn_(planet)
• uranus_(planet)
• venus_(planet)

See also

• asteroid
• comet
• moon
• moon_(celestial_body)
• space
• planet destruction