SVN
From The DarkMod Wiki
So what is this SVN thingy then?
SVN stands for SubVersioN. It's a framework originally developed for distributed coding projects, often with multiple programmers working on the code at the same time.
The Dark Mod is a project distributed over the whole world, that's where SVN comes in handy. It allows all Team Members to work on the Mod at the same time without coming in the way of each other.
DarkMod SVN Infrastructure
You lost me there, I need an example!
All right then, here you go: SVN Tutorial
SVN Glossary
The SVN terminology can be confusing at times, this is a (probably incomplete) list of terms explained: SVN Glossary