It is an advanced separation and coiling drill, a literal twist on top of the classic Touch the outside boot drill used everywhere: while touching the outside boot, twist the upper body to the outside of the turn so the inside hand points to the outside of the turn. The idea is that the shoulders are facing down the fall line when the skis are crossing the slope.
You can also think of it as a more advanced version of the The Schlopy Drill.
This gives you a lot of critical elements of great skiing:
Start doing this earlier and earlier, until right in transition and stay in this position through the turn. Then progress to and refine it by moving progressively and continuously throughout the turn.
Many kids and beginners/intermediates have a lot of problems doing this drill properly, so here's a progression to here:
As a progression from here, you can:
A note on the "twist" to the outside: it should be progressive: a little at the beginning of the turn and finish with the skis sideways crossing the slope while the upper body is facing down the slope - that is an extreme position great for racing, but we get good by averaging out the extremes :)
Read more drill ideas.