CVS (Concurrent Versions System) is a version control system that can record the history of your files (usually, but not always, source code). CVS only stores the differences between versions, instead of every version of every file you have ever created. CVS also keeps a log of who, when, and why changes occurred.
CVS is very helpful for managing releases and controlling the concurrent editing of source files among multiple authors. Instead of providing version control for a collection of files in a single directory, CVS provides version control for a hierarchical collection of directories consisting of revision controlled files. These directories and files can then be combined together to form a software release.