The ability to forage, hunt, create shelter, and similarly fairly handy skills in avoiding dying while away from civilization. This is the individual that can tell the party which brightly colored berries are safe to eat, and lie to someone they don't like to cause wacky fatal hijinks.
Survival is also used in tests of ruggedness and endurance, such as determining whether you can stay conscious when very injured, and even to avoid death when critically wounded. Because of its literal life-or-death applications, it's classified as a combat skill for costs.
0: Are these berries poisonous? Who knows! Let's hope for the best.
1: You have a decent chance of building a fire without starting the Great Gray Forest Fire.
2: Competent enough to survive in the wilderness under normal conditions and less likely to be eaten by a bear.
3: You're able to be hired as a guide by nobles wanting to go 'glamping', and can debate whether to lead them into shav territory.
4: Outlaws fleeing in the woods hate being tracked by someone this good.
5: In the heart of a roaring blizzard, you're sent out to rescue someone.
6: Wolves ask you for wilderness survival tips.