At a given stage of development, giving one or more files a common label that refers to their revisions, is known as tagging those files. Tagging is typically used on entire modules, so that the current state of the module can be reconstructed in the future. This kind of tagging should always be done on project deliverables, and before starting major changes.
To tag one or more files or directories with a label, select the directory, file or files that you want to tag. Right-click the mouse button on the selection, and choose the CVS → Tag... menu item.
You will then be presented with the Tag Dialog. Here you can enter a label in the Tag field. CVS is quite restrictive when it comes to what characters a tag may contain. A tag must start with a letter, and may contain letters, digits, "-" (dash) and "_" (underscore) only. In particular, this means no dots, and no spaces. If you want to include version numbers in a tag, replace the dots with dashes. Two tag names are reserved, as they have special meaning in CVS: "HEAD" refers to the most recent version available in the repository, while "BASE" is the revision you last checked out into the local directory.
Once the label has been entered, press the OK button. Unlike most CVS operations, the tag is immediately applied to the repository, and no commit is required.
For more information see Making a Snapshot: CVS Tag....