Head Restraint Geometry: The relationship between an occupant's head and neck and the head restraint in the vehicle they are traveling in; usually in terms of “backset” and “topset”.

Homeostasis: This is the tendency to maintain, or the maintenance of, normal, internal stability in an organism by coordinated responses of the organ systems that automatically compensate for changes in the organism. All systems strive for a state of homeostasis or balance.

Hypoesthesia/Hypesthesia: An increased sensitivity to nerve stimulation.