title: what does reachable/unreachable mean in git?
body: <p>Little bit confused..</p>
  
  <p>In the <a href="http://book.git-scm.com/3_reviewing_history_-_git_log.html">git community manual</a>, it says </p>
  
  <blockquote>
    <p>The git log command can show lists of
    commits. On its own, it shows all
    commits reachable from the parent
    commit; but you can also make more
    specific requests</p>
  </blockquote>
  
  <pre><code>$ git log v2.5.. # commits since (not reachable from) v2.5
  </code></pre>
  
  <p>I thought git log by itself only shows you the commits made to the current branch, and the commits are sequential - so how can you have one commit made since another, but unreachable from it? </p>
  
  <p>I think I'm either misuderstanding what git log does or what unreachable means or both.. grateful for any help!</p>