Definition of terrestrial planet in English English dictionary
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
a planet having a compact rocky surface like the Earth's; the four innermost planets in the solar system
Any of the four planets, Mercury, Venus, Earth, or Mars, that are nearest the sun and have similar size and density