The International Astronomical Union (IAU) defines a planet as a celestial body that:
1. Orbits the Sun.
2. Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.
3. Has cleared the neighborhood around its orbit.
Ganymede meets the second criterion but fails the first and third. It orbits Jupiter, not the Sun, and shares its orbit with other moons and objects.
Therefore, Ganymede is classified as a moon or satellite of Jupiter.
