Understanding the apt-get sources.list

Hi -

I have done some preliminary research on the apt-get command from https://help.ubuntu.com/community/Re...es/CommandLine

So I understand when I type something like: apt-get install nessus
The interface will reference the /dev/apt/sources.list file to determine where to find the package file for Nessus, will retrieve the package, and then install the application. I noticed that when I ran the command, however, it installed Nessus v 4.4.1, while the most recent version is somewhere in the 5.x range. My original, unedited, sources.list file contains the following:

deb http://all.repository.backtrack-linux.org revolution main microverse non-free testing
deb http://32.repository.backtrack-linux.org revolution main microverse non-free testing
deb http://source.repository.backtrack-linux.org revolution main microverse non-free testing

Can someone explain to me, or refer me to a website that explains what these words mean after the URL: "revolution main microverse non-free testing"
I am trying to figure out how BT5 R3 determined that it should install an older version of Nessus. I'm really trying to understand the workings of the apt-get command better.

Thanks for any help!

While this is a fairly beginners question on Linux and isn't really specific to Backtrack.

I would recommend you do some more research on "repositories" and how they work :) you can find a lot of documentation online about this for different distributions.