While the term 'gnar' may get used a lot by freeskiiers, it isn't a term exclusive to skiing.
Urban Dictionary gives it two meanings:
1. A shortened version of the word gnarly, meaning high on the scale of dangerousness and coolness. Often used among the skateboard crowd
"That switch heelflip was gnar"
2. Snow.The white stuff. You like it.
"Lets shread the gnar"
These are both very applicable to skiing, but it's a term also used in other 'extreme' sports.
gnar is anything and everything
I don't know the slang term for a guitar but the slang term for playing the guitar is "shredding the gnar" so I'd imagine that the slang term is gnar.
Gnar stands for Gonkey's Numerical assessment of Rad. Invented by Shane McConkey, this is like a game that is played on ski slopes. The term Gnar is used by skaters, skiers, and surfers, or any sport in which something might be radical. For more info on the original watch "The Game of G.N.A.R." at unofficialnetworks.com or read the rules in the book Squallywood.
It can also be called Nordic Skiing...
Traversing means skiing back and forth across the fall line
Slalom is the name given to water skiing with one ski.
This term refers to the sport of skiing.
Workaholics - 2011 The Future Is Gnar 3-20 is rated/received certificates of: Netherlands:12
gnar wall-e
It means a sunny blue sky day with fresh powder snow... perfect skiing conditions.
Nordic skiing: The Scandinavian tradition of skiing, which includes cross-country skiing as one of its disciplines, is referred to by this name. Skiing XC: Cross-country is commonly abbreviated as XC when referring to the sport. Touring on skis: Cross-country skiing in mountainous terrain, in which skiers traverse uphill and downhill to explore backcountry areas, is frequently referred to by this term. Langlauf: Cross-country skiing is frequently referred to as a "langlauf," which translates to "long run," in German-speaking regions. Skiing in a traditional manner: One of the two primary approaches to cross-country skiing, along with skate skiing, is the classic style. Cross-country skiing can be distinguished from skate skiing by referring to it as "skiing in the classic style."
'Skiing' is a term used to describe the sexual position where a boy (or a girl) gets between two guys, while facing in the same direction, and jerks them both off, thus imitating cross-country skiing.