Revision Control (sometimes called Configuration Control) is the process of recording changes to a set of files as they are edited over time, and aiding the management of parallel changes by multiple authors. By far the most common use of revision control systems is in software development, where they also have the name Source Control Management systems (or SCM).
The basic concepts of revision control systems, common to most of them, are documented here:
RevisionControlConcepts/CheckInOut – Basic usage for most SCMs
RevisionControlConcepts/Branching – Multiple development lines
RevisionControlConcepts/Tags – Coherent sets of revisions
There is a huge number of different revision control systems. The articles below each give a brief introduction to some of the more common (or interesting) ones.
More information about SCMs and a basic comparison between them all can be found at The Better SCM Initiative.