title: iOS SDK: Working with NSUserDefaults
body: <p>With the <code>NSUserDefaults</code> class, you can save settings and properties related to application or user data. </p>
  
  <p>now i have tow question : </p>
  
  <ol>
  <li><p>( settings and properties ) Where are stored ? 
  if =>The objects will be saved in what is known as the iOS “defaults system" 
  then : What is iOS “defaults system" </p></li>
  <li><p>How long will remain stored ?</p></li>
  </ol>