What does the acronym “BASE” in the sport of BASE jumping refer to?

BASE jumping is a recreational sport which consists of plunging or jumping from fixed objects, using a parachute to descend safely.

The word "BASE" is an acronym that stands for the four types of fixed objects from which a participant might jump: Buildings, Antennae (radio towers), Spans (bridges), and Earth (cliffs, canyon rims, etc.). The jumper leaps from the chosen fixed object, and after an optional freefall delay, which depends on the height of the starting point, the individual deploys a parachute to slow their descent and land.

Jumping pioneer Carl Boenish (1941-1984) co-invented the sport, along with his wife Jean Boenish, Phil Smith, and Phil Mayfield, in the late ’70s and early ‘80s, and helped come up with the name. (The initial acronym, B.A.S.E., was eventually shortened to BASE.) An accomplished photographer and skydiver, Boenish’s first plunge into the sport was a jump from the 3,000-foot summit of El Capitan in Yosemite National Park, USA.

BASE jumping offers a unique challenge. Unlike skydiving from airplanes, since BASE jumps originate at significantly lower altitudes, they afford a quicker, shorter freefall, which in turn leaves a narrower window for successful parachute deployment. For this reason, BASE jumping is deemed significantly more hazardous than other forms of parachuting, and is widely considered to be one of the deadliest sports in the world.

* Boenish died in a BASE jump in Norway, in April of 1984.