SCUBA is an acronym for "Self Contained Underwater Breathing Apparatus". In short, scuba diving is strapping a tank of air to your back out of which you can breathe air so you won't drown. SCUBA was co-invented by Jacques Cousteau and Emile Gagnan in 1943 as the Aqua-lung.
One global organization for Scuba Diving is PADI, who can be seen at http://www.padi.com/
It's worth noting that people interested in Scuba diving should first find out all the ways to die:
- The bends
- Lung problems
- Running out of air