The term for the distance from the Earth's center to its surface is "radius." The average radius of the Earth is about 6,371 kilometers (3,959 miles). This measurement can slightly vary depending on whether one measures from the equator or the poles due to the Earth's shape, which is not a perfect sphere but an oblate spheroid—wider at the equator and slightly flattened at the poles. Understanding the Earth's radius is essential for various scientific fields, including geology, geography, and astronomy, as it helps in calculations related to gravity, the Earth's atmosphere, and satellite orbits.