"Planetary" refers to anything related to planets, which are large celestial bodies that orbit stars, including our own Sun. Planets can be classified into two main types: terrestrial planets, like Earth and Mars, which have solid surfaces, and gas giants, like Jupiter and Saturn, which are composed mostly of gases. In addition to their physical characteristics, planets can also be studied in terms of their atmospheres, climates, and potential for supporting life. The study of planets is a key part of astronomy, helping scientists understand the formation of our solar system and the possibility of life beyond Earth.