A.k.a. supplemental nudge; it refers to where you give someone's hip an assistive push with your hip to shift him over in a bench-seat when he is unable to do so under his own power, such as if he is totally exhausted, if he has a huge lapful of objects, or if the floor is not clear/flat/level enough for him to brace his feet solidly against it and slide himself over.
Trying to effectively brace one's feet and scooch over into the middle of the seat far enough to make room for a third person can be difficult in a pickup truck with a floor-mounted manual shift-lever and transmission-hump in the way, so the entering passenger may be obliged to give said middle-rider a helpful hip-nudge to slide him over the rest of the way so that the entering passenger can seat himself and shut the truck's door.
by QuacksO April 8, 2019