I really hate to be obnoxious about it, but Talentless and Mobil1 are the only people in this thread who have any idea what they are talking about. I've never seen such misuse of definitions.
Drifting: this has to be defined as "exhibition" or "Japanese" drifting. In other words, tuning for excessive oversteer, and putting the car sideways for its own sake. Because it has nothing to do with real drifting (see below). Exhibition drifting requires that the rear wheels have lost traction, either fromm heavy braking or being overpowered. This is what makes it flashy but very slow.
Powersliding: a type of exhibition drifting, in which the car is driven to oversteer by applying power to the rear wheels. Once countersteering is cranked in, the car is balanced with the throttle. It has nothing to do with how many wheels have lost traction. In fact, you better have traction at the front end of the car or you're about to visit the ditch.
Four wheel drift: real drifting, as correctly described by Mobil1, is a cornereing technique developed in the early, pre-aero days of Grand Prix racing. In "drifting" a turn, all four tires are at the limit of adhesion - but no wheels have lost traction. All four tires are crabbing slightly - moving forward and slightly sideways at the same time, with the rear tires crabbing slightly more than the fronts. This allows the car to rotate through the turn at high speed, with the front wheels pointed straight ahead, also as described by Mobil1. Throttle control is critical here, too, but not for the purpose of keeping the car sideways. Four wheel drifting is the fastest way to take a turn, because you maintain limits traction throughout. With smooth inputs and careful balance, you can maximize the amount of braking/cornering at the entry, and the amount of acceleration/cornering at the exit.
Now, everybody on board? Great!