lol, a wrap deformer is like a lattice but you define the cage yourself with geometry.

So lets say you have a high res character that continually requires updates and changes frequently. Now rather than binding this mesh to the joints directly, a lower poly version of the character that has been modified to fit around the high res character can be bound tothe joints, then a wrap deformer can be used to have the low res bound mesh drive the high res mesh.

look it up in the help docs, for details on usage. It saves huge time on skinning since you dont have to deal with the details, and when you make changes to the high res sculpt there is far less work to do.