Well I am not going to probably be able to express this in the most eloquent way...but it is simply being able to master turning around a turn/curve in a controlled slide manner.
In drifting you turn DUE TO your slide while power sliding is only sliding due to your turn (or power on at the end).
For an idea...go to
http://www.driftworks.org/ and then click on videos and watch a few of the clips...they are not big or long. It will give you an idea. In Japan this is an art form b/c it's bringing your car to the brink of losing grip and control but not...and for people who know...drifting sometimes is not the fastest way around a turn...only around really tight ones would I say that drifting is faster. The better you get at drifting...the higher speeds you can take and so forth. There's plenty of drift videos out there...that show canyon runs where there are lines of cars drifting or industrial park drifting where there is also a line of cars just go through the turns drifting...
Hence from this...a drift car would most likely be a RWD car although it is possible to "slide" not drift a FWD car...AWD cars can do this but in the USA...we really dont have that many RWD or AWD cars...but I've named a few up top.