http://blog.easybranches.com/activity-streams/p/843207/ <a href="http://cristy2493yp.drupalgardens.com/content/exactly-what-are-%E0%B8%A3%E0%B8%B1%E0%B8%9A%E0%B8%97%E0%B8%B3-web-optimization">straight from the source</a>