Drift Diving is basically going with the flow or riding in the current of the underwater super highways that are frequented by many types of marine life.
Drift diving looks fun and easy, however it does require developing certain skills to maintain control in the flow, breaking techniques as well as techniques for ascending and descending in the current.
Drift diving is said to be one of the most rewarding diving techniques to learn. The technique of drift diving calls for you to ignore all that you have been taught as it relates to swimming against the current and just sit back and take a ride, so to speak. That is, depending upon the speed of the current, you often don't have to use your fins to propel yourself forward. The technique is quite useful in areas with strong currents that can be difficult to swim against.
Drift diving requires an extra measure of caution. It is important to do this type of diving in a dive site that you know very well. You must carefully plan your exit points. It can't be emphasized enough, currents can be strong and take you out into deep water or force you under, so know your dive site well.
Drift dives typically follow along walls, wrecks, shorelines or reefs. Bali has some amazingly beautiful drift diving sites around the island of Nusa Penida as pointed out by a post on baliocean.com