Git prompt is a third-party contribution to the git repository that enables users to use tab completion for common git commands. According to git completion creator Shawn O. Pearce, completion support is provided for:

1. local and remote branch names
2. local and remote tag names
3. .git/remotes file names
4. git 'subcommands'
5. git email aliases for git-send-email
6. tree paths within 'ref:path/to/file' expressions
7. file paths within current working directory and index
8. common --long-options

This functionality is provided by shell scripts for bash, tcsh and zsh. Each of these shell scripts can be downloaded here:

https://github.com/git/git/tree/master/contrib/completion