Earth is the planet on which we live, the 3rd planet from the Sun. Questions using this tag should be about Earth the planet and not Earth-like planets nor earth, as in dirt or soil.
Earth is the 3rd planet from the Sun, one of the 4 terrestrial planets (i.e., "rocky planets") in the solar system (the remaining 4 planets are gas giants). It is currently the only known planet to harbor life.
Different fields of science study Earth, including,