Default Setting
The "default setting" of D&D is the context that is implied by the Rules As Written. This doesn't refer to any specific fantasy world, like Greyhawk or Mystara. Rather, it takes the "core rules" as a whole and explores the implications and assumptions inherent in such a system. This article in the D&D wiki is a great example: "D&D represents a period in history that is most closely identifiable with the Iron Age: the landscape is dotted with tribes and aspiring empires, the wilderness is largely unexplored, and powerful individuals and small groups can take over an area without having a big geopolitical hubbub about it." In my opinion, it also closely resembles the Wild West (or rather, its fictional depiction) but with swords and sorcery instead of six-shooters. When adventurers reach "name level" they will tend to migrate to the frontier of civilization to establish their stronghold in unclaimed territory. The discovery o...