A system capable of recording the changes made to a file or a set of files over a time period in such a way that it allows us to get back in time from the future to recall a specific version of that file, is called a version control system.

To give you a more formal explanation, a version control system is a software package that when initiated will monitor your files for changes and allow you to tag the changes at different levels so that you can revisit those tagged stages whenever needed.

When installed and initiated, this version control system creates a local directory at the same place where your files reside, which it uses to manage the entire history of the changes made to your files.