title: Why staging directory is also called Index/Git Index?
body: <p>I was confused the naming of staging directory (Git Index) in Git. </p>
  
  <p>Is there any special meaning such that it is called Index?
  Why not just called Cache / or Temp directory so that we can understand more easily?</p>
  
  <p>To me, index is sth which help us to search things faster, like indexing in DBMS, 
  how does it relate to the staging area???</p>
  
  <p>I did some google search but still have no much idea. 
  ref link <a href="http://book.git-scm.com/7_the_git_index.html" rel="noreferrer">Git Index</a></p>