The geoid is a term scientists use to refer to Earth’s actual irregular shape. While it’s commonly known as a sphere, it’s not a perfect one, being slightly flattened at the poles and slightly bulging at the equator because of Earth’s rotation; this is known as an oblate spheroid. While this is a more accurate description of Earth’s shape than a perfect sphere, the geoid goes a step further by taking into account gravity’s effect and the distribution of mass, “essentially depicting a state where all the oceans are calm and at rest.”