Geoid vs. Spheroid

Geoidnoun

The shape that the surface of the oceans of the Earth would take under the influence of the Earth's gravity and rotation alone, extending also through the continents, disregarding other factors such as winds and tides; that is, a surface of constant gravitational potential at zero elevation.

Spheroidadjective

Of a shape similar to a squashed sphere.

Geoid

The geoid () is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended through the continents (such as with very narrow hypothetical canals).

Spheroidnoun

A solid of revolution generated by rotating an ellipse about its major (prolate), or minor (oblate) axis.

‘UFOs are reported as being either oblate (saucer-shaped) or prolate (cigar-shaped) spheroids.’;

Spheroidnoun

A body or figure approaching to a sphere, but not perfectly spherical; esp., a solid generated by the revolution of an ellipse about one of its axes.

Spheroidnoun

a shape that is generated by rotating an ellipse around one of its axes;

‘it looked like a sphere but on closer examination I saw it was really a spheroid’;

Spheroid

A spheroid, also known as ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has circular symmetry.