"Lean Six Sigma is a melding of Six Sigma components with those from Lean Manufacturing. While Six Sigma focuses on the quality of the final product or service, Lean is primarily concerned with speed and the elimination of waste and unnecessary steps. In Lean Six Sigma, these two approaches are consolidated in recognition that both speed and quality are important." (Michele McDonough, 2009)
This quote comes from the Bright Hub website (http://www.brighthub.com/) and can be found in the Business section. The article is answering the top six questions about Six Sigma and one of the questions is what's the difference between Six Sigma and Lean Six Sigma?
Basically the most common answer is that Lean focuses on the production of a product or service and Six Sigma works on the production as well as the final product/service itself. Whatever is going to be in the customer's hands is what Six Sigma tries to improve. This answer can be compared to the answer above.