Progressive- adjective- favoring or advocating progress, change, improvement or reform, as opposed to wishing that things remain as they are.
the term, in skiing, is generally used to refer to what could be called 'Skiing After Snowboarding'... the changes in ski gear has allowed for changes in technique. Prior to snowboarding 'expert' skiers were skiing 203 to 210+ cm skis, the most difficult terrain was mogul runs and steep skiing consisted of hop turns and hip checks. Now skiers are skiing much shorter skis that are much wider, new terrain has been added to most ski areas, there is more grooming on piste and there is more terrain off piste, skiers flow with the terrain instead of imposing a rigid turn shape onto the terrain. Terrain parks have bred a new generation of skiers who can do some pretty darn mind-blowing stuff in the air.
I'd say 'Progressive Forms' would be characterized by smooth fluid skiing and aerial maneuvers which work with the terrain and gravity.
non Progressive would be characterized by rigidity in line, turn shape and effort to 'resist' gravity.
Obviously not all progressive skiing is better than old-school skiing, it honestly requires less fine skill but more raw athleticism, it's just a new movement in the sport which is trying to put their generation's stamp on the sport they love.