1911 Encyclopædia Britannica/Geoid

GEOID (from Gr. γῆ, the earth), an imaginary surface employed by geodesists which has the property that every element of it is perpendicular to the plumb-line where that line cuts it. Compared with the “spheroid of reference” the surface of the geoid is in general depressed over the oceans and raised over the great land masses. (See Earth, Figure of the.)