The Mickey Mouse universe is a fictional shared universe which is the setting for stories involving Disney cartoon characters, including Mickey and Minnie Mouse, Donald and Daisy Duck, Pluto and Goofy as the primary members, and many other characters related to them, being most of them anthropomorphic animals. The universe originated from the Mickey Mouse animated short films produced by Disney starting in 1928, although its first consistent version was created by Floyd Gottfredson in the Mickey Mouse newspaper comic strip. Real-world versions also exist in Disneyland and Tokyo Disneyland, called Mickey's Toontown.
Butch (left) along with Pluto in his debut in Bone Trouble
A shared universe or shared world is a fictional universe from a set of creative works where one or more writers independently contribute works that can stand alone but fits into the joint development of the storyline, characters, or world of the overall project. It is common in genres like science fiction. It differs from collaborative writing in which multiple artists are working together on the same work and from crossovers where the works and characters are independent except for a single meeting.
Early example: Captain Marvel and Bulletman join forces to battle Captain Nazi, thereby establishing a shared continuity within the Fawcett "universe".