title: Meaning of numbers in "col-md-4"," col-xs-1", "col-lg-2" in Bootstrap
body: <p>I am confused with the grid system in the new Bootstrap, particularly these classes:</p>
  
  <pre><code>col-lg-*
  col-md-*
  col-xs-*
  </code></pre>
  
  <p>(where * represents some number).</p>
  
  <p>Can anyone please explain the following:</p>
  
  <ol>
  <li><strong><em>How</strong> that number is aligning the grids?</em></li>
  <li><strong><em>How</strong> to use these numbers?</em></li>
  <li><strong><em>What</strong> they actually represent?</em></li>
  </ol>