Any planet of the solar system or any exoplanet which is "Earth-like" in the sense that it is composed primarily of metals and rock, in contrast to a planet which is a gas giant.

(astronomy) A planet which orbits in the habitable zone around a star, where temperatures like those on Earth occur, allowing for the possible existence of liquid water and of life.

the planet Mars

Any of the four gas giant planets in the Solar System: Jupiter, Uranus, Saturn, or Neptune.

(astronomy) A world-like planetoid of the Solar system, that is smaller than the classical planets. More specifically, any astronomical body which has a geology defined by hydrostatic equilibrium (and thus has taken the shape a body of water would take, as opposed to a small Solar System body), orbits the Sun (as opposed to a moon), and does not gravitationally dominate other bodies near its orbit (as opposed to a classical planet or, in IAU usage, as opposed to a planet).

(astronomy) A hypothetical planet in the Solar system, beyond the currently known outermost planet. (The term was applied to Eris for a short while, when Pluto was still considered the ninth planet.)

(planetology) a planet that flies through interstellar space and has no star to encircle

(science fiction) homeworld

(astrology) A planet thought to bring bad luck to those born within its radius

Used other than figuratively or idiomatically: see tertiary, planet. (the third planet; usually counting outwards from the central sun)