A "stem" is the action of one ski that changes the relationship of the skis from being parallel to being in a wedge (or snowplow). A stem can be done with either the uphill (usual as in the old stem-christy) or downhill ski (abstem). A stem is usually the first move of 1-2 sequencial rotary pushoff initiation to start a turn as opposed to using a parallel initiation.
There is probably a German or Austrian translation to this effect.
A plough is used to turn over dirt in a field. Seriously though a "snowplow" is the ancestor of the wedge, using a wider displacement of the ski tails, what we would now call a "braking wedge" (vs. a narrower gliding wedge). It was called such being shaped like the "V" blade of a snowplow, and probably because it enabled less skilled skiers to plow through the ungroomed snow of the era in which it origionated, in that they could not yet ski parallel in those conditions on 7' wooden skis with low-cut leather boots. Which justified it's role in the learning pathway 60 years ago. As for now with modern equipment, knowing what we know? I wonder if we were to reinvent learning to ski today, starting with a blank sheet and open minds (and the customers bests interests at heart), if we would even remotely consider the wedge as a primary pathway, or simply acknowledge it as an alternative when needed?