Git Directory / Git Working Trees / Git Index

What are they? What is the relationship among them?

Git Directory is the '.git' directory in the root of your project. It contains all the meta information and Git's history for your project. You can go to .git directory and type in command 'tree -L 1' to show all the files/directories inside it.

http://book.git-scm.com/1_git_directory_and_working_directory.html

Git Working Tree is not Git Directory. The working tree is basically a tree of all the HEAD commits. Each HEAD commit is a node in that tree.

http://www.kernel.org/pub/software/scm/git/docs/user-manual.html#def_working_tree

Git Index is a staging area between your working directory and your repository. When you create a commit, what is committed is what is currently in the index (a file), not what is in your working directory.

http://book.git-scm.com/1_the_git_index.html A working directory is your current checkout files. Ultimate reference: Git User Manual