The Displace modifier in 3ds Max acts as a force field to push and reshape an object's geometry. You can apply its variable force directly from the modifier gizmo, or from a bitmapped image. The 3D Studio Max displace modifier works on Shapes, Meshes, Polys, Patches, NURBS. Displace is often used to make terrains or to add finer texture to 3D models with out having to model in extra texture. It can also be used in a very controlled way to manipulate geometries. With the use of procedural texture maps or bitmaps one can can make large scale manipulation to geometry with minimal effort. See how powerful a tool the displace modifier is in thie 3ds Max tutorial from David Fano.