3.x E was Greyhawk, 4e had it's own new cosmology, I cant seem to find out what 5e's default universe/setting is
The core rules don't really have a default setting aside from the "D&D Multiverse" (in that it refers to multiple published settings, and assumes the use of the Great Wheel cosmology). However, the published adventures have all (except for Curse of Strahd) have been set in the Forgotten Realms.
I'd say "official" is nothing, but "default" is Forgotten Realms, if I were to distinguish between the two terms.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.