Acording to Wikipedia (you gotta love Wikipedia) Backcountry skiing is skiing in a sparsely inhabited rural region over ungroomed and unmarked slopes or pistes, including skiing in unmarked or unpatrolled areas either within the ski resort's boundaries or in the backcountry, frequently amongst trees ("glade skiing"), usually in pursuit of fresh fallen snow, known as powder.

More importantly, the land and the snow pack are not monitored, patrolled, or maintained. Fixed mechanical means of ascent such as ski lifts are typically not present, but may be used to gain initial altitude.

Backcountry skiing, ski touring or ski mountaineering can involve single or multi-day trips through snow camping or the use of mountain huts where available.

I was intruduced to backcountry skiing when I was living in Truckee, California. We often go to Mt. Judah, Castle Peak, Sunrise Bowl, Fallen Lake near lake Tahoe and other places in Sierra Nevada.