Answer:
Isostatic rebound is actually a very slow adjustment process among the terrestrial elastic layers of planets like earth, which gets slower once it reaches certain equilibrium.
It's defined as a rebound due to the response after a very heavy force/load is either removed or further inflicted on the lithosphere, depresing it or displacing it, and making it rise up again somewhere else.
The pression or load/force is caused by huge ice sheets, such as when ice ages in the past, which can either melt at some point in time, or reach equilibrium, with the asthenosphere (layer below lithosphere) gathering enough strengh to carry that weight.
In both scenarios, the earth's response is slow and it may vary either due to it's axial tilt and orbit related to the Sun causing warmer periods, or to the changes in weight upon the lithosphere, just like Skandinavia which is still rising back up from the last ice age.
Explanation:
