The Overworld is the first world in the videogame of Minecraft.
The Overworld is created by default upon creating a new world. Other dimensions, such as the Nether and the End, will only be created upon accessing the proper portals.
New worlds in Minecraft are generated through the use of seeds, which are typically a random number that is used as a starting point for the world generation formula. If given a non-integer input (such as the word "Glacier"), the seed input is converted into the corresponding integer (such as 1772835215).
Seeds will generate almost exactly the same world every time, given the same game version and the same world type. Although the exact spawn point varies, the coordinates of all terrain features will remain the same.