Isostatic refers to a balance or equilibrium of forces acting on something. It means that the force pushing down from above is equal to the upward force from below, creating a stable condition. Full definition
«Palaeoshoreline records of glacial isostatic adjustment in the Dry Valleys region, Antarctica.» (polenet.org)
Observation of glacial isostatic adjustment in «stable» North America with GPS. (nature.com)
Measured GMSL was corrected for the effects of Glacial Isostatic Adjustment with a global model, which increased the GMSL rate by 0.25 mm / y (25). (pnas.org)