title: What is the difference between ACL and user roles in Symfony2
body: <p>I am new to symfony2 and i am confused with the terms and what is use case for these.
  can anyone please explain what is the difference between</p>
  
  <ol>
  <li>ACL</li>
  <li>Roles</li>
  <li>Groups</li>
  </ol>