The terms "inferior planet" and "superior planet" were originally used in the geocentric cosmology of Claudius Ptolemy to differentiate those planets (Mercury and Venus) that were between the stationary Earth and the orbiting Sun from those planets (Mars, Jupiter, and Saturn), which lay beyond the Sun's orbit. In the 16th century, the terms were modified by Copernicus, who rejected Ptolemy's geocentric model, to distinguish a planet's orbit's size in relation to the Earth's. The terms are sometimes used more generally: for instance, the Earth is an inferior planet as seen from Mars.

This classification should not be confused with the terms inner and outer planet, which designate those planets which lie inside the asteroid belt and those that lie outside it, respectively. "Inferior planet" should also not be confused with the very different minor planet or dwarf planet.

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