Ubuntu 20.04 LTS Focal
Ubuntu Package Repositories:
Ubuntu package repositories are basically file servers where all the deb packages are kept.
Ubuntu has 4 main official package repositories: main, restricted, universe, and multiverse.
In main repository, Ubuntu supported free and open source softwares are kept.
In restricted repository, proprietary drivers (i.e. NVIDIA) are kept.
In universe repository, free and open-source softwares that are maintained by the community are kept.
In multiverse repository, softwares that have copyright restriction or legal issues are kept.