Diving is jumping or falling into water. It can also mean swimming beneath the surface of the water.
Kristin was injured twice while diving off the Cliffs of Heaven in a recreation of Sumiko IV on the holodeck. (TNG: "Conundrum")
See also: Orbital skydiving.
Skindiving is diving without a wetsuit, using a snorkel. Once, Geordi La Forge went skindiving off the coral reef on Bracas V. He would later relate this experience when the Enterprise was being pulled through space by what appeared to be a school of two-dimensional lifeforms. (TNG: "The Loss")
Scuba diving is diving with special self-contained breathing equipment.
Scotty used a force field instead of a normal wetsuit and breathing apparatus when diving on planet Argo.
A holo-program exists called "Scuba Diving, Hanauma Bay, Earth". (TNG: "The Emissary")
Charles Tucker III was an experienced scuba diver. He kept a picture of himself scuba diving in his crew quarters on Enterprise, as well as an antique diving helmet. (ENT: "These Are the Voyages...")