There are a lot of articles on the net explaining the differences between Agile Vs Lean. There are eternal debates about them too. But this article AgileVersusLean by Martin Fowler gives the most simplistic explanation about the subject.
In the above article, Martin ends by saying I think of lean as a strand of thinking within the agile community, like a pattern in a rich carpet.
Picture courtesy: http://www.popgadget.net/2008/02/flexible_hanger.php