What term describes a shape that resembles a sphere but is slightly flattened at the poles?

The term that describes a shape resembling a sphere but slightly flattened at the poles is referred to as an oblate ellipsoid. This term is used in geodesy and geophysics to characterize the shape of the Earth. An oblate ellipsoid is defined mathematically as a solid shape that is generated by rotating an ellipse about its shorter axis, leading to a shape that is wider at the equator and narrower at the poles.

In the context of the Earth's geometry, this is significant since the Earth is not a perfect sphere due to its rotation, which causes it to bulge at the equator. The oblateness of the Earth affects various geospatial calculations and models, making it important for accurate mapping and positioning.

A geoid represents mean sea level adjusted for gravitational variations and does not represent a simple geometric shape like an oblate ellipsoid does. A reference ellipsoid serves as a mathematically defined shape used as a model for the Earth's surface, but the phrasing "slightly flattened at the poles" specifically describes the oblate nature. A sphere lacks the flattening characteristic and thus is not the fitting term in this context.