terestrial

Terestrial (often spelled terrestrial) is an adjective relating to Earth. It is derived from Latin terrestris from terra, meaning earth. The standard modern spelling is terrestrial; terestrial appears as a less common variant or historical spelling.

In biology and ecology, terrestrial describes land-dwelling organisms or ecosystems. Terrestrial animals and plants live on the land rather than in water or air. Terrestrial ecosystems include forests, grasslands, deserts, and tundra, and they contrast with aquatic or aerial environments. In astronomy, terrestrial planets are rocky planets with solid surfaces, such as Mercury, Venus, Earth, and Mars, as opposed to gas giants.

The term also appears in other technical contexts. Terrestrial radiation refers to heat or electromagnetic radiation originating from the Earth. In geodesy and navigation, terrestrial reference frames describe positions relative to the Earth's surface, standardized for measurements and mapping. The word is often contrasted with extraterrestrial, meaning originating outside Earth.