Hiking is an activity; friluftsliv is a category defined by what it excludes — no engines, no competition. It's also formal public life rather than a hobby: the right to walk and camp on uncultivated land regardless of ownership was written into Norwegian statute in 1957. English keeps the walking and drops the ethic and the legal right that makes it possible.
Side by side
Aspect
Friluftsliv
Hiking
Is
A category
An activity
Excludes engines
By definition
No opinion
Excludes competition
Yes (Sweden)
No
Backed by statute
Yes, 1957
No
What each one means
Friluftsliv
Friluftsliv is Norwegian and Swedish for outdoor life in your free time, especially in forest and open country. Norwegian policy narrows it further — under your own power, no engines — and there it's a legal and planning category, not a mood.