In astronomy, Inferior Planet refers specifically to Mercury and Venus because both orbit the Sun inside Earth’s orbit. From Earth, they therefore always appear relatively close to the Sun in the sky and can never appear opposite the Sun. The term describes a planet’s orbital position relative to Earth, not its size, importance, or physical characteristics. It should not be confused with Inner Planet, which commonly refers to the four terrestrial planets Mercury, Venus, Earth, and Mars. Mercury and Venus are therefore both Inner Planets and Inferior Planets, while Mars is an Inner Planet but a Superior Planet.
AKA / Related Terms:
Sometimes described as a planet interior to Earth’s orbit
Related to Inner Planet, but the terms are not synonyms
Opposite classification: Superior Planet