The Earth is not perfectly spherical. It's actually an oblate spheroid. This means it's a sphere that is slightly flattened at the poles and bulging at the equator.

Here's a breakdown:

* Sphere: A perfectly round shape where every point on the surface is equidistant from the center.

* Spheroid: A slightly flattened or elongated sphere.

* Oblate spheroid: A spheroid that is flattened at the poles and bulging at the equator.

The Earth's equatorial diameter is about 43 kilometers (27 miles) larger than its polar diameter. This slight difference is caused by the centrifugal force generated by the Earth's rotation.

While we often use the term "sphere" to describe the Earth, it's more accurate to use the term "oblate spheroid" to describe its shape.