One of the most helpful yet underused facilities of CVS is the tag. CVS's tagging feature allows you to label a revision for later retrieval. This feature also allows you to fork development so that you can work on two or more versions of your project simultaneously. The version that has been forked off is called a branch, and the main line of development is called the trunk.
This chapter explains tags, branches, and how to merge branches and trunks. It also discusses why and when to branch and provides strategies and hints for using branches effectively in your project.