Lean Six Sigma is the combination of Lean and Six Sigma into a single business philosophy.
Lean is commonly thought of as a way to improve process speed. Six Sigma is primarily considered a quality tool. In truth, though, the two both share a lot of the same tools, and both focus heavily on problem solving.
Combining the two into Lean Six Sigma was a logical step to leverage the strengths of both. In fact, many people had already been doing just that, but without specifically apply the label ‘Lean Six Sigma’.