SVN or Subversion is a software control system for tracking software changes. It is similar to
Concurrent Version System.
What it means is there is a central site that you check in and check out versions of your robot software. That way you can track what changes are made. It works well if you have 2 or more developers. They can all work on the software and put their changes in. You can roll back to prior versions if you find that something did not work the way you expected it to.
Even single developers will find it useful for the roll back features.