Short for Concurrent Versions System, an open-source, network-transparent program that allows developers to keep track of different development versions of source code. CVS does not maintain multiple versions of source code files but keeps a single copy and records of all of the changes that are made. When a developer wants a particular development version of a file, CVS will reconstruct that version based on its records. Bugs can often get into code when it is modified and may not be detected until long after the modification is made. CVS can retrieve old versions of the code, allowing the developer to see precisely which change caused the bug. CVS is also useful when more than one person is working on a specific file, where it is possible for the developers to overwrite each other's changes. CVS solves this problem by having each developer work in an individual directory and then merging the work from each after the work is complete.
It is important to note that CVS is not a build system but rather a way to control disparate versions of code as it is developed over time.
CVS is also called a version control system.