I am currently writing a research paper on Linked games, a thing that I will probably be talking about more in the future (topic of my PhD). However, as a part of the process, I am explaining different terms and showing them through examples. As an interesting fact, I decided to use the game of Zelda to define what is the difference between Game World and a Game Universe.
The main difference (at least by our definition) is that Game World is the place where a single game takes place. All the characters, locations and events within that one game happen in the same World. The player can affect the way where the world goes and what happens to the characters in the world.
As a separation to this, a Game Universe is something that contains joint elements between multiple games. For example Final Fantasy Universe has similar characters, such as chocobos and moogles, even though the world where the gameplay happens is different in each game. Even better example (and the one I wanted to illustrate here) is the Universe of Zelda games.
All the Zelda games have same characters, the hero Link, princess Zelda, evil Ganondorf and so on. The place where the game takes place is called Kingdom of Hyrule and some items, such as Master Sword are known fact in all of the games of the franchise. However, the game world is not geographically the same (of course, this is also due to the limits of different game consoles, graphics, and so on), but still the games can be seen happening in the same storytelling universe. No matter how many times Link saves Zelda and defeats evil Ganon, the events seem to be forgotten/lost in the next game. Still, this is totally okay for the storytelling, as the universe is the same.
I want to illustrate the evolution of Zelda universe through few map screenshots:
Somehow different, yet still makes sense😀