CVS (Concurrent Version System) allows many people to work together on the same code. The CVS Server keeps track of the original code and all modifications commited to the server by poeple working on the code. By checking out a CVS module from the server, you can get the code and update the code you are working on with the latest changes to the code on the CVS server. If you are a developer with CVS "write access" you can also check in or "commit" your modifications to the server.