Lean Vs. Six Sigma Vs. Operational Excellence

To "Get Lean", "Six Sigma a Process", or "Achieve Operational Excellence", are all hot buzzwords being tossed around organizations today to incite continuous improvement efforts, but what are the differences between them? and can they be used interchangeably?

Lean
To address Lean itself is to streamline a business or manufacturing process. The approach is used to reduce cycle times, decrease process waste, and remove bottlenecks. This generally comes in the form of identifying and attacking the 7 deadly wastes (TIMWOOD):

• Transport - This refers to the movement of product not people. Transportation of product comes at a cost and takes time. 
• Inventory - This refers to either Work In Progress (WIP) materials for Finished Product (FP) that is just sitting around. Storing items takes up real estate which comes at a cost.
• Motion - This refers to movement of people within a process. Getting up to fetch materials or performing the same action where a jig could be designed is wasted effort and time.
• Waiting - Waiting for information, machines, or previous process item all contributes to cycle time.
• Overproduction - Overproduction is simply product the customer is not willing to pay for and represent unwarranted work and stress on the process.
• Over-processing - This represents added and superfluous work that the customer is not willing to pay for. 
• Defects - This refers to added cost of producing product not within specifications and includes efforts to correct these issues.

Six Sigma
Six Sigma methodology is concerned mainly with quality. The sigma level of a process refers to the ability of a process to run defect-free. Six Sigma in particular represents an operation that produces fewer than 3.4 defects per million opportunities. Coordinating this level of quality requires an assortment of tools and techniques involving statistical analysis and process controls to reduce variation in the system. Most Six Sigma projects are performed in 5 phases: Design, Measure, Analyze, Improve, Control (DMAIC).  

Operational Excellence
Operational Excellence (or Op-Ex) represents the management philosophy behind creating and sustaining a workplace culture around continuous improvement and meeting performance metrics. Operational Excellence includes aggregating and aligning all corporate activities with a singular goal. While you can argue that Lean and Six Sigma fall under the purview of Op-Ex, it is not comprehensive. To achieve Op-Ex is to sustain a system that ensures all facets and levels of the organization work towards continuous improvement. However, not all Op-Ex activities may have to do with reducing costs or increasing flow. Instead, Op-Ex could be used to innovate and build value. 

Conclusion
All these terms relate to continuous improvement but each vary slightly by definition. Lean and Six Sigma go hand-in-hand and are generally used in tandem as an approach although it is important to understand the main motivations of each. Operational Excellence is often used to describe Six Sigma and Lean activities but it is more related to the support system orbiting Lean Six Sigma initiatives.