Vertex skinning
The deformation step of skeletal animation: each vertex is moved by a weighted blend of its bones' matrices.
Skeletal animation decides the bones' poses; skinning is the math that makes the skin follow. Each vertex carries up to four bone indices and as many weights, and its final position is the weighted sum of the bone matrices applied to the rest pose. The standard method is called linear blend skinning (LBS) and is, at heart, a weighted average.
LBS is fast but pinches at bent joints — the infamous "candy wrapper" elbow where volume collapses. Dual quaternion skinning (Kavan et al., 2007) preserves volume better at a higher cost. Since the early 2000s the blend has run in the vertex shader on the GPU ("hardware skinning"), freeing the CPU from touching every vertex once per frame.