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. Wikipedia

Irregular surface approximating the mean sea level Wikidata

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. Wiktionary

Surface of constant gravitational potential at zero elevation. Wiktionary (translation)