Flight (舞空術, Bukujutsu; Literally meaning "Sky Dance Technique") is one of the most commonly used techniques in the Dragon Ball series. The result of it is that the user manipulates their ki energy so that they can levitate or fly. This is first seen in Dragon Ball during the first appearance of Puar, and first named during the 22nd World Martial Arts Tournament, when Tien Shinhan and Chiaotzu are seen flying. Very soon all the other Z Fighters (apart from Yajirobe) use the technique.
In the original Japanese dub of episode 3 of Dragon Ball Z, "The World's Strongest Team", when Goku asks if Piccolo can keep up with the Flying Nimbus, the Namekian replies that his own flying technique is significantly different and better than the flight technique used by the Z Fighters, allowing him to fly faster than the Nimbus.
Gohan is able to teach Goten and Videl how to fly during the Great Saiyaman Saga. Gohan further explains that anyone with sufficient power and the proper training can learn the ability. Mr. Satan tries to self-teach this technique but fails miserably.
The way Gohan describes the secret to Flight, one would assume that the flyer is putting their ki underneath them, and riding it in a manner similar to the Flying Nimbus. However, whether this is actually how it works, or if it was a result of Gohan not knowing a better way to describe it, is unexplained.