This was certainly true when I was a kid, and "universe" meant "all existing matter and space (observable or not)". As a youtube-couch expert on astrophysics,

This was certainly true when I was a kid, and "universe" meant "all existing matter and space (observable or not)". As a youtube-couch expert on astrophysics, I hear "universe" redefined as something like "a bubble of matter and spacetime that is 'quarantined' and can never communicate with the rest of the cosmos" whenever multiverse theory is discussed.