Pragmatic Guide to Git

18	Tagging Milestones

You need to make milestones in your projects, each slightly different, such as for one, its weekly iterations, and for another, its version numbers. You can use git tag to handle this.

git tag creates a read-only marker within the repository. You can treat tags like branch names, except you can’t check them out and start committing to them. You can create a new branch from a tag, however.

Creating a tag requires one parameter: the name of the tag. Nearly every character you can use as part of a filename on Unix systems can be used as part of a tag name. You cannot use the characters ^, *, or :, and a tag cannot begin or end with /.

You can create a tag from a commit other than HEAD by supplying a second parameter ...