"Skiing is not a sport, it is a way of life." -Otto Schniebs
Sports are defined by competition, rules, and organization. If you are competing or training to compete, skiing is a sport. If you are not competing or training to compete, it is outdoor recreation. There are varying levels of physical demand and prowess from couch potato to peak level. But without competition, rules, and organization, an activity cannot be considered a sport. Examples: hockey is a sport, skating is not, baseball is a sport, throwing a ball is not, etc. You can throw a ball or skate at a very high level, but in isolation without competitors and organization, these are physical activities not sports.