GEOLDE derived from the Greek GUEIA, 'earth' and from EIDOS, 'form', 'appearance'; error by GEOIDE, body defined by the equipotential surface of the Earth's gravity field. It is an approximate model of the true shape of the Earth with its flattening at the poles, as a consequence of the gravitational force applied to the differential masses that exist in the direction of the vertical axis of the planet.