B.A.S.E. - An acronym
BASE jumping is the sport of using a parachute to jump from fixed objects and are generally made from much lower altitudes than skydives.
BASE is an acronym that stands for the four categories of objects which one can jump;
Buildings - Antenna - Span - Earth
To achieve your BASE number you need to jump from each of the four objects. Base number 1 was given in 1981, Dan's number is BASE782.