I'm not exactly sure but:
-fast race base
-good sidewall construction
-sharp durable edges
-laterally stiff (you don't want any chatter at the speeds racers are going)
-torsionally stiff (this with the addition of sidewall construction allows the ski to hold a solid edge and not boot out or skid out when making an aggressive turn on super hardpack or icy snow)
-various lengths and sidecut profiles depending on the discipline (slalom, gs, super g, downhill, ski cross)