barycenter A center of gravity created between selected elements.  


closed primitive A closed surface on which a weight can be applied. It can be a sphere, a cylinder, a box, a pyramid or a torus.  


open primitive An open surface made of several faces. It can be rectangular, circular, triangular or ring-shaped.  


subdivision An algorithmic technique to generate smooth surfaces as a sequence of successively refined polyhedral meshes.  
subdivision surface A skin made of an elementary surface, that can be closed or opened.
The definition and the control of the shape is made using a mesh. This mesh is made of four-sided faces.