A skeleton hierarchy is composed of a series of joints and joints chains with hierarchical relationships. Each joint in a skeleton hierarchy is a child joint and a parent joint.
A parent joint is any joint higher in a skeleton’s hierarchy than any of the other joints that are influenced by that joint’s actions. Joints below a parent joint in the skeleton hierarchy are called child joints. Joints at the top of bones are always parents, and joints at the bottom of bones are always children. Parent joints drive the transformations of their respective child joints. Thus, when you translate or rotate a parent joint, you also translate or rotate all of its child joints.
The root joint is the highest joint in a skeleton’s hierarchy. A skeleton can have only one root joint. You can move and orient the entire skeleton in world space by translating and rotating the root joint.
