(1) According to the theory of isostasy, the balancing of masses above and below the geoid so that vertical pressure in regions close to the surface is approximately constant regardless of the elevation or depth of the physical surface. Such regions are said to be in isostatic equilibrium. If all parts of the region are in isostatic equilibrium, compensation is said to be local; if isostatic equilibrium holds for the region as a whole but not for parts of the region, compensation is said to be regional. The terms completely compensated and undercompensated are applied to compensation in such regions. (2) The quantity: (1 - (average isostatic anomaly))/(average Bouguer anomaly).