Quite a bit is different. The gear is different, the skis are straight, as opposed to downhill skis being curved (the curve makes it easier to turn on a downhill slope), the boots in cross country are not stationary in the bindings, as downhill boots are, instead you can move the heels, and the poles used in cross country are longer. Also, the slopes are not nearly as steep as in downhill skiing.
if there is friction on the hill it will slow you down
skiing is......... going down hill on snow using skies to guid you
aerobic.
Snowsport
when you are skiing down a hill and you want to slow down
*Cross country* skiing is where you are skiing on flat terrain. It's much more work than skiing down a hill.
Down Hill Skiing
slalom
the judges score on how fast you go down the hill.
Ski bas d'une colline
That loosely describes skiing.
Back country skiing is where one hikes to the crest of a hill, and alpines down. A type of skiing similar to back country skiing is telemark skiing. Back country skiing has no synonyms.