US Military term to describe one's head. It is a mocking of the Four points of contact during a parachute landing fall taught to soldiers in Airborne school at Fort Benning Georgia. It is used in many ways, though mostly used in negative ways. If you do not properly execute a Parachute Landing Fall or PLF, one will often hit their head, which is how the term developed.
It is often heard from the Airbone School instructors, or 'black Hats' whenever a student hits their head as in 'Nice use of that 5th point of contact', or 'only use the four points of contact, do not use the fifth!' It can also be used in a military slang term 'You better pull your 5th point of contact out of your 3rd point of contact!' Which means, Pull one's head (5th point of contact) out of their own ass (which in a PLF is the 3rd point of contact) or in a more verbose sense, you better unfuck yourself.