Ski touring broadly refers to skiing across open terrain. Ski touring evolved from cross-country skiing (also known as Nordic skiing), a popular sport and recreational activity. Cross-country ski equipment is quite light to provide good mobility. Cross-country skis mostly don’t have metal edges and can be difficult to turn when skiing on icy snow and slopes.
Backcountry skiing broadly refers to skiing terrain in remote areas with a focus on skiing up and descending steeper slopes. Ski equipment used for backcountry skiing is often heavier and provides better control and turning when skiing down hills. Backcountry skis with sharp metal edges provide better ski control, particularly on steep and icy slopes.
Frontcountry is terrain that is off-trail but within ski area boundaries where ski lifts and emergency services are close at hand.
Slackcountry is terrain outside of marked ski area boundaries and accessed from a lift without having to use skins or a boot trail. A route may finish back at a resort or at road to access a car shuttle.
Sidecountry is terrain outside ski area boundaries that is accessible via a ski lift.
Alpine touring refers to backcountry skiing in remote areas using Alpine Touring (AT) equipment. The term originated in Europe where the use of AT equipment is very popular. In France Alpine Touring is also known as Ski randonnée.
Backcountry snowboarding is a very popular activity using a snowboard or splitboard to travel in the backcountry.
Ski mountaineering involves additional equipment including ropes, ice axes, crampons, harness, carabiners and other mountaineering equipment. This equipment is used for glacier travel, climbing steep icy passes (cols) and summits.
NOTE: Specific training is needed to use mountaineering equipment safely - a mountaineering course or guided trips are recommended for novices.
Ski touring - Wikipedia