The occipital ridge is the region at the back of the head where the base of the skull

Human skull

The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...

 meets the spine

Vertebral column

In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

.

This general area is quite vulnerable, and as such offensive maneuvers (esp. in martial arts

Martial arts

Martial arts are extensive systems of codified practices and traditions of combat, practiced for a variety of reasons, including self-defense, competition, physical health and fitness, as well as mental and spiritual development....

) have been created to target the occipital ridge. If the occipital ridge is hit with sufficient force, it will cause immediate blackout. Only trained combatants should consider this tactic as a mistake is capable of causing death.