A Concurrent Versions System (CVS) repository is a persistent data store that coordinates multi-user access to projects and their contents. Projects in a repository can be of two forms: immutable (a project version) or modifiable (a project in a branch). Communication between the repository and Workbench clients is possible over local or wide area networks. Currently the Workbench supports two internal authentication protocols for CVS: pserver and ssh. Authentication protocols provided by external tools can also be used by CVS.
You can find more information on CVS at https://directory.fsf.org/wiki/CVS.