title: What does dirty/clean working directory mean?
body: <p>From Version Control with Git by Leoliger 2ed,</p>
  
  <blockquote>
    <p>After you commit the addition of the new file into the repository, git status indicates
    that there are no outstanding, staged changes to be committed.</p>
  
  <pre><code> $ git status
   # On branch master
   nothing to commit (working directory clean)
  </code></pre>
    
    <p>Git also takes the time to tell you that <strong>your working directory is clean</strong>, which means
    the working directory has no <strong>unknown</strong> or <strong>modified</strong> files that differ from what is in the
    repository.</p>
  </blockquote>
  
  <p>Does "modified" files mean the same as tracked files that are modified but uncommitted? Does "tracked files" mean files that have been committed before?</p>
  
  <p>What does "unknown" files mean? </p>
  
  <p>Does ignored files not count?</p>
  
  <p>Does untracked but not ignored files count as "unknown"?</p>
  
  <p>Btw, in Pro Git by Chacon:</p>
  
  <blockquote>
  <pre><code>$ git status
  On branch master
  nothing to commit, working directory clean
  </code></pre>
  </blockquote>
  
  <p>This means you have a clean working directory – in other words, there are no
  <strong>tracked and modified</strong> files.</p>