Skeleton and Forward/Inverse Kinematics
Skeleton	A skeleton is a hierarchical articulated structure of joints. It is used for posing and animating deformable objects that is bound (skinned) to the structure.
Root joint	A root joint (start joint) is the highest joint in a skeleton's hierarchy.  A skeleton can have only one root joint, while it can have multiple chains of joints.
Forward  kinematics	Forward Kinematics (FK) is a method of animating a skeleton where the animator specifies rotation angles for each joint in the hierarchy.  When a joint is rotated, all the joints lower in the hierarchy follow.
Inverse  kinematics	Inverse Kinematics (IK) is a method of animating a skeleton where the animator specifies only the position of the end effector, and the computer calculates all the intermediate joint angles.
End effector	An end effector is the end point in a chain of joints.