BASE jumping is a form of sport parachuting involving parachuting off a fixed object. BASE stands for the four types of fixed objects: Buildings, Antennas, Spans (or bridges), and Earth formations such as cliffs and canyon rims.
Relation to skydiving
BASE jumping is considered a separate sport from skydiving, because skydiving involves falling through airspace and the use of aircraft, all of which fall under the regulation of government agencies such as the U.S. Federal Aviation Administration and place skydiving within the broader realm of aviation. BASE jumping falls outside of this realm. For this reason, sport parachuting organizations such as the USPA (United States Parachute Association) do not concern themselves with BASE jumping.
However, skydiving is the usual entry route into BASE jumping, and most BASE jumpers were highly experienced skydivers before attempting their first BASE jump.
BASE jumping is considered a highly dangerous sport, because of the low altitudes one jumps from. These are far lower than in most sport parachuting and in many cases do not allow sufficient time to deploy a reserve parachute, should the main chute fail to deploy.
Another danger comes from the likelihood of collision with an object, such as a canyon wall or the side of a building, while falling. BASE jumpers have to be expertly skilled at both direction control during freefall and canopy control.
Still another danger comes from the fact that BASE jumping may also involve illegally trespassing onto private property and then having an escape plan to avoid arrest after the jump. This is especially the case at most skyscrapers, antennas, and U.S. National Parks which do not welcome nor desire BASE jumpers.