Skating crossovers is simply skating along a curved path while still stroking. To do this, you have to cross the outer skate over the other one and hence the term "crossover". Done properly, a crossover will not only let you maintain your speed going into the turn, but also let you increase it to an extent. The turns that ice speedskaters do during the Olympics are all crossover turns. Figure skaters will often do backwards crossovers during their routines, and hockey players do a variety of both during games.