The Donald Duck Universe or The Scrooge McDuck Universe or simply The Duck Universe is a popular fan-made term by people who like to keep the Ducks and Mice separate. However on this wiki there are no separate Duck Universe characters.
Some fans have even argued that there have been instances where Disney did not want to do “crossovers” between the Ducks and Mice. However, Disney makes it quite plain that it’s all in the same world, by the fact that many of the characters (including minor ones) from the Duck comics and television shows have met Mickey Mouse. They also have made it clear that they view Duck centered programs (such as DuckTales the reboot and Darkwing Duck) as sub-franchises to the main Mickey and Friends franchise, by the fact that they are categorized under the latter on the official Disney Store website. So please refrain from using that fan-made term if possible.