Concurrent Versions System (CVS)
CVS is a system that lets groups of people work simultaneously on groups of files. A version control system keeps a history of the changes made to a set of files. For a developer, that means being able to keep track of all the changes you've made to a program during the entire time you've been developing it.
CVS clients communicate with CVS servers over a local area network or the internet (in general: a TCP/IP based network). When you use a CVS client, it sends your data and CVS commands to the server and receives new data and results from the server and stores or displays them on your client machine.