Skinning; Embellished Articulated Skeletons

In computer graphics, a skeleton is often dressed up with more complex geometry, e.g., representing  muscles or skin.
This is typically deformable geometry.
Each part (every vertex) of this embellishment geometry needs to bie tied to at least one of the links, so that it can move with it.
Near joints, some vertices in the transition zone may be tied to more than one link, so that they some intermediary position
and smoothly blend between the geometry portions that are attached only to a single link. 

Let's look at an enlarged portion of our mannequin:

When a link in the skeleton moves moved, all skin vertices that are completely (or partially) attached to it must also be updated.
The movements of the various links to which a skin vertex is attached are summed up in an appropriately weighted fractions.