I've been peeking into the ubuntu respository and I see four folders, multiverse, universe, restricted and main. What do they represent?
From the Ubuntu documentation:
The repository components are:
Main - Officially supported software.
Restricted - Supported software that is not available under a completely free license.
Universe - Community maintained software, i.e. not officially supported software.
Multiverse - Software that is not free.
For example:
The Ubuntu Desktop team manages the gnome-terminal package, it is officially supported and in the main repository.
bcmwl-kernel-source (the Broadcom wireless driver) is in restricted, since it is a supported, but proprietary, driver.
Community written software that is not officially supported (for example, the game supertuxkart) is in the universe repository.
Packages like ubuntu-restricted-extras (which contains proprietary codecs that allow you to play media files, including flash player) are in the multiverse repository because they are not free and their restrictive licenses prevent inclusion in the default package set.
From Wikipedia:-
