"Minecraft" uses world-generation seeds to tell the world-creation algorithm how to go about building the map. Entering the same seed value generates the same map. "Minecraft" first added village generation into the world creation algorithm in version 1.8 of the beta release.
Procedural generation is the use of a mathematical algorithm to create content such as music, images or video-game graphics. In the context of "Minecraft," it allows the game to have a much smaller download size, and saves incalculable time for the game's creator. There is no feasible way for the game's developer to make by hand each of the trillions upon trillions of possible maps the 32-character seed code allows.