The Brush > Elasticity sub-palette controls the elasticity of the brush.
The Elasticity Strength will control the amount of strength that will be used to maintain the geometry of a mesh while it is being edited.
The Auto Adjust Effects the strength of the elasticity as you move your stroke back to the starting point.
Tip : Use the move brush with elasticity and pull a piece of the surface away from the mesh, them move your brush back to the starting point to see how this will effect the shape you create in the surface. Then adjust the elasticityautoadjust to see this effect changes when moving back to your strokes starting point.
The Auto Off will determine what polycount can be reached for a mesh before ZBrush will automatically disable the elasticity settings. Once the polycount has been reach any brush with an Elasticity Strength on it will take on the same behavior it had before Elasticity was applied.
Reference Guide > Brush> Elasticity