The hollow at the base of the throat. Also called the jugular notch, it is found as a small notch at the top of the sternum. In self-defense, a person may thrust their fingers into the suprasternal notch, using straight and downward pressure. This maneuver induces choking and/or unconsciousness through blockage/crushing of the windpipe.
Fun Fact: A thrusting attack to the suprasternal notch was choreographed into the subway station fight scene in the movie The Matrix.
Learn more at Wikipedia.