Shape keys and hooks are great ways to deform a mesh, but the problem with them is that both are lacking a good underlying structure. They're great for big, cartoony stretching and deformation, but for a more structured deformation, like an arm bending at the elbow joint, the motion that they produce is pretty unnatural looking. To solve this problem, 3D computer animation took a page from one of its meatspace contemporaries, stop-motion animation. Stop-motion animation involves small sculptures that typically feature a metal skeleton underneath them, referred to as an armature. The armature gives the model both structure and a mechanism for making and holding poses. Blender has the same structure and it, too, is called an armature. Armatures form the basis of nearly all Blender rigs.
To add an armature to your scene, go to the 3D View and press Shift+AArmatureSingle Bone. As Figure 11-7 shows, adding an armature creates a single object with a weird shape called an octahedron. Continuing to use the skeleton analogy, that octahedron is referred to as a bone in the armature. The wide end of the bone is referred to as the bone's head or root, and its narrow end is referred to as the bone's tail or tip. Typically, a bone pivots at the head.