Equatorial radius, in the context of planets, refers to the distance from the center of a planet to its equator. It is a measurement that characterizes the planet's size and shape, specifically along its equatorial region.

The equatorial radius is an essential parameter used to describe the planet's overall dimensions and is typically expressed in units of kilometers (km) or miles (mi). It represents the distance from the planet's core to the point on its equator that is farthest from the planet's center.

The equatorial radius of a planet is influenced by various factors, including its rotation, gravitational forces, and internal composition. Planets are generally oblate spheroids, meaning they are slightly flattened at the poles and bulging at the equator due to their rotation. As a result, the equatorial radius is larger than the polar radius.

For example, Earth has an equatorial radius of approximately 6,378 kilometers (3,963 miles), while its polar radius is about 6,357 kilometers (3,950 miles). This small difference between the equatorial and polar radii is due to Earth's relatively rapid rotation, causing a noticeable bulge at the equator.