BASE is an acronym for the four categories of fixed object jumped from: Building, Antenna, Span (bridges) and Earth (cliffs). BASE jumping is parachuting from these rather than from an aircraft.
Why it is not skydiving
BASE jumps happen at low altitude with no time for a reserve, and the equipment reflects that: a single canopy, configured for very fast opening. Proximity to the object introduces hazards that do not exist in the sky.
It is substantially more dangerous than skydiving and is a different activity, not an advanced version of the same one.
It is not taught at drop zones
Drop zones do not teach BASE. The conventional path is extensive skydiving experience first — commonly several hundred jumps at minimum — followed by a dedicated first-jump course from BASE-specific instructors.
This entry exists because the term comes up constantly in skydiving contexts. It is not an encouragement, and nothing here is guidance.
These pages explain what things are so the language makes sense. They are not instruction and cannot substitute for it — skydiving is taught in person by rated instructors at a drop zone, and anything involving equipment handling or emergency procedures belongs there rather than on a web page.