A "fictional universe" refers to an imaginary world or setting created by a writer or artist. It is a place where fictional stories, characters, and events take place. Think of it like a make-believe world with its own rules and elements.
So in spite of it being confirmed that it and GTA take place in the same fictional universe, don't expect any crossovers with cities we've seen before. (rdr2.com)
Her love of video games and the stories they told are what inspired her to write her own stories, and she has been building fictional universe ever since. (enchantedbookpromotions.com)
Either way, it's direct confirmation that the two games take place in the same fictional universe. (tomsguide.com)