We might, following Einstein, say a universe is an inertial space where the laws of physics are uniform in all directions. If there is another inertial space with different laws of physics, it would be a different universe. That is, defining universe as 'all there is' would do away with regimes of physical laws and destroy some possible utility of the word. The term 'world' could remain as 'all there is,' or we might use the neologism 'multiverse,' which ought to be reserved for further possibilities IMHO.