A derisive term used by skydivers to denote an individual who does not participate in the great sport of skydiving. The, most likely apocryphal origin of the term is as follows:
A skydiver lands in a farmer's field, begins gathering up his canopy, and heads back towards the road. He encounters a farmer who gives him a long, contemplative look before asking, "Plane on fire?"
"No," responds the skydiver, bemused.
"Well," the farmer pauses, brows furrowed in thought, "whuffo you jump?"