This is a prominent bump at the base of the cervical spine. it is usually the (Prominent) spinous process of seventh cervical Vertebra, though in some people the 6th cervical or 1st thoracic is most palpable.


This is really a point of orientation: it signifies the transition from neck to torso (bottom of the cervical level to the top of the thoracic)

Mohan (http://www.cfp.ca/cgi/reprint/52/12/1549) says that tenderness here is a sign of depression.