FFD stands for free-form
deformation. It is used in computer animation for effects
like dancing cars and gas tanks. You can use it as well for modeling rounded
shapes such as chairs and sculpture.
modifier surrounds the selected geometry
with a lattice box or cylinder. By adjusting the control points
of the lattice, you deform the enclosed geometry.
You can use
control an FFD space warp. Physique actually deforms the space warp's
which in turn deform the model.