An overworld is, in a broad sense, an area within a video game that interconnects all its levels or locations.
Hyrule Field for The Legend of Zelda.
The Elder Scrolls series boast some of the largest Overworlds in gaming.
In The Elder Scrolls III: Morrowind, the Vvardenfell island is a single continuous explorable location, dotted with countless entrances to smaller dungeon and indoors levels.
The Elder Scrolls IV: Oblivion is similar to Morrowind'', except that entire cities are also rendered as smaller sub-levels accessible from the overworld.
Unc. n. 1.) A place in a videogame where levels, or other areas of the overworld, are connected; a hub.
Unc. n. 2.) A location in a videogame that takes place on or above the ground, or, more generally, anywhere within the natural world.
A) Above ground.
B) Anywhere that is not (considered) supernatural.
Adj. 3.) Pertaining to the sections of a game that take place above ground or within the game's "natural" world.
"The original Super Mario Bros. did not have an overworld-map."
"Donkey Kong Country, for the most part, takes place in the overworld."
"One block in the nether is eight blocks in the overworld."
"I love the overworld music in New Super Mario Bros. Wii!"
When Drake breeds with Minecraft dragons.
OMG, look at the Overworld Drake!