fourth point of contact

fourth point of contact
 n.— «I had no problem climbing onto the bed of the truck, since I was ten pounds lighter in my fourth point of contact.…p. 394: The fourth point of contact when performing a parachute landing fall is the buttocks.» —by Richard R. Burns Pathfinder: First In, Last Out Feb. 26, 2002. (source: Double-Tongued Dictionary)