Gill--this is a great question. Unfortunately, as with so many things, a simple, brief answer can't do it justice! Different kinds of turns finish in different ways.
In the "old days," all turning on skis boiled down to one simple sequence: doing something to break the skis out of their straight line tracks and into a skid, then controlling that skid, and finally, ENDING that skid. Different techniques all related to the various ways these things could be done.
For all turns that involve throwing the skis into a skid, even today, finishing the turn still means stopping the skid, thereby setting up the solid platform from which to throw the skis into a skid the other way. That means, usually, increasing the edge angle of the ski(s) and perhaps increasing the pressure on the tail(s)--an "edge set."
For these "old" turns, the traditional division into "initiation, control, and completion" phases makes sense. (We also identify a "preparation phase," prior to initiation, which coincides with the completion phase when turns are linked without a traverse.) But things CAN be different today.
I often use the analogy of driving a car, and I'll bring it up again here. How do you "finish" a turn in a car? Assuming that the tail didn't fishtail out into a skid, all you have to do is stop steering the wheels into the turn--straighten them out--right? And starting the next turn is just a question of steering them the other way. Smooth and seamless. There are no distinct phases, as described above. (Of course, if a skid is involved, either intentionally or not, the turn resembles the skidded skiing turns above--the skid must be started, controlled, and stopped.)
By the way--as the issue of defining exactly where a single, linked turn starts and stops has just come up again in another thread, for this discussion, I'm defining the stop/start point as the transition from turning one direction to the other--from an arc that takes you to your right, to an arc that takes you to your left--the moment the car's wheels point straight ahead. From a traverse, the turn starts the moment you start turning downhill, and ends when you finish turning and start traversing across the other way.
So a carved
turn starts the moment the edge(s) release. When the new edge(s) engage, the ski(s) bend and carve through the arc, perhaps aided by active steering movements of the feet and legs. Here' the key: if turns are linked, the end of one turn marks the start of the next. Therefore, the turn also ENDS the moment the edge(s) release! The answer to your question, then, might surprise you, Gill: You finish the turn by flattening your ski(s), ending the carving effect of an edged, pressured ski. Note that this is just the opposite of the edge set that ends a skidded turn!
A modern turn begins and--if linked--ENDS in "neutral." For a smooth, flowing linkage in modern turns, you could say that there IS no beginning or end. All the way through the turn, you must move in such a way that you "arrive in neutral" at the exact spot you intend for the turn to end. You can't wait 'till the end to "start finishing" the turn. This is the mistake many skiers make. They release their edges to start, and progressively tip them more and more as they go through the turn. Then they decide it's time to finish the turn, and it's too late! Often they are squatted down low and "angulated," and stuck in the back seat at the "end" of the turn, rather than balanced, "neutral," and moving into the new turn.
In other words, if (and only if) you have done everything "right," you don't have to do ANYTHING to finish a modern, high-performance turn--or to start the next! It's just a continuation of the flow of movement that you've been guiding constantly, throughout the turn. If you have to do something in particular to get out of the turn, it's a sign of something wrong earlier--or perhaps throughout!
At this point, I'll refer you to a couple other threads where we discussed the technique of modern ski turns in great detail (click on the links):How do you make a perfect turn?
In the "illustrated" thread, look closely at the sequences--any of them will do, although the Parallel Turn sequences show the biggest range of motion, so the movements may be more obvious. Study also the edge angle graphics, which show the skis tipping progressively (relative to the slope) through the turn, then "untipping" as the end approaches, finishing the turn flat on the snow, in "neutral."
One continuous, cyclical movement--that's the signature of contemporary high-performance turns. It's hard to break it down into distinct phases. If I had to, I'd describe a "transition phase," encompassing "neutral," an "edge & pressure increase" phase, and an "edge and pressure decrease" phase. But even these phases overlap and flow seamlessly together.
Words cannot describe....