Level 5 takes full autonomy to "all driving modes." That means the car is fully capable of driving itself anywhere in any condition, from a snowy, moonlit road to an unmapped desert. It should be noted that, at this point, Level 5 is theoretical. One Audi representative went so far as to describe it as "mythical." It's unlikely we'll see Level 5 autonomous driving in our lifetimes.
Level 4 is definitely obtainable though.