When you want to install new software or updates to already installed Ubuntu software, by default Ubuntu provides four different software repositories to get it from. These repositories are Main, Universe, Restricted, and Multiverse. Maybe you have wondered what’s behind their cryptic names. Here is what each of these represent.
See https://www.maketecheasier.com/multiverse-universe-restricted-main-repositories-ubuntu/ 
Differences Between Multiverse, Universe, Restricted & Main Repositories
If you are a Ubuntu user, you have seen the different repositories: Main, Universe, Restricted, and Multiverse. Here is what each of these represent.