There is no official rules on what is and is not drifting, but these are the parameters I hold true.
First I would like to point out that ANY TIME YOU ARE MOVING IN A FORWARD DIRECTION AT AN ANGLE TO THE DIRECTION THE CAR IS MOVING YOU ARE IN A DRIFT. Other than that these are the ways that I justify a drift, or take the drift badge away from the slide.
* denotes that there is an exception to the rule
1. *You are on a paved surface, not dirt or grass, or wall riding, *
2. If you are going at least 5mph the entire time of the slide,
3. *You have atleast 5 degrees of angle the entire time of the slide, *
4. *You ARE STILL SOMWHAT IN CONTROL OF THE CAR DURING THE SLIDE, *
5. *You did not spin out at any time during the slide, this would also violate #3, *
That is it, notice that there is an exception for all of them except for #2 as you MUST be moving forward in some way, shape, or form to be drifting, you can't drift at a stand still.
Also notice that the type of initiation, the amount of angle above 5*, the amount (if any) of wheelspin, NONE OF THIS MATTERS FOR THE ACT OF DRIFTING. If you are talking about the organized sport of drifting, then they all have different rule books determinining drift scores and safety regulations and what not. Go to D1GP.com, FormulaD.com, etc.
Exception to #1: If you only get off the road for a second or two, or only get two wheels off, then you are still drifting as long as the majority of the slide was on a paved surface. As for wall riding if you lightly tap a wall in a way that doesn't/wouldn't do major damage in real life, a light wall tap is considered a drift technique to some people.
Exception to #3: If you immediately start sliding in the opposite direction, then that is considered a link drift and the drift continues on. Once you fall below 5* without linking, the drift ended at that point, it also started at the point the slide iinitially hit 5*. The length of your drift is the distance between these two points.
Exception to #4: If you loose control but then regain it again, it is still counted as a drift as long as all the other conditions/exceptions were satisfied.
Exception to #5: Pulling a 360 into, out of, or during a drift is concidered drifting as long as all the other conditions/exceptions were satisfied. Same goes for beyond 90* angle drifting.
Sorry it was so long, but you asked for it.