Answer:
It is the collarbone.
Also see "what is the function of the clavicle."
In human anatomy, the clavicle or collar bone is classified as a flat bone that makes up part of the shoulder girdle (pectoral girdle). It receives its name from the Latin clavicula ("little key") because the bone rotates along its axis like a key when the shoulder is abducted. (This movement is palpable with the opposite hand). In some people, particularly females who may have less fat in this region, the location of the bone is clearly visible as it creates a bulge in the skin.
Clavicle is the medical term for collar bone.