I read wilderness as, "places sapient folk haven't had much impact on." The forest and bog not too far from the village? Where the hunters and poachers go? Sure, nobody's rightly settled there, but people impact it and utilise it. Deeper, it speaks to me about how elves interact with their environs, cause I'd guess that their homes are largely still wild, and they do what they can to live as part of the cycle, where dwarves and orcs, humans and halflings just pain rape the land and leave it touched. The elf is far more comfortable navigating the untouched places, or those only touched by elven hands, because that is how things are "supposed to be." Anyway, my two cents.
Edit: for a much more boring answer, "anything more than a few days from the nearest settlement," but I dislike that answer. Cause it's boring.