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A Lean Six Sigma Glossary

Lean Six Sigma has developed its own vocabulary to express its underlying concepts and operational processes. Here are definitions of the some of the more commonly used terms. Because of Lean’s origins in Japan, Japanese equivalent terms are shown in parentheses in some cases.

The “5 Whys.” The “5 Whys” typically refers to the practice of asking 5 times why a failure has occurred in order to get to the root cause of any problem. Of course, a problem can have more than one cause. Generally, root cause analysis is carried out by a team of people who are related to the problem. No special technique is required.

The “5S’s.” Five terms beginning with “S” are used to create a workplace suited for visual control and Lean production.

  • Sort (Seiri). Eliminate everything that is not required for the current process and keep only the bare essentials.
  • Straighten (Seiton). Arrange all items so that they are easily visible and accessible.
  • Shine (Seiso). Clean everything, and find ways to keep everything clean. Make cleaning a part of everyday work habits.
  • Standardize (Seiketsu). Create rules by which the first three S’s are maintained.
  • Sustain (Shitsuke). Keep 5S activities from unraveling.

Balanced scorecard. This is a strategic management system used to drive performance and accountability. It balances traditional performance measures with more forward-looking indicators, such as finances, integration and operational excellence, employees, and customers.

Benchmarking. This is an improvement process that an organization uses to compare its performance against best-in-class companies. It then uses the information gathered to improve its own performance. Subjects that can be benchmarked include strategies, products, programs, services, operations, processes, and procedures.

Black Belt. Six Sigma team leaders responsible for implementing process improvement projects to increase customer satisfaction levels and business productivity are known as “Black Belts.” They are knowledgeable and skilled in the use of Six Sigma methodology and tools, typically have completed 4 weeks of training, and have demonstrated a mastery of the subject matter through the completion of projects and an examination.

Cell. A cell is a group of people, machines, materials, and methods arranged so that processing steps are located adjacent to each other and in sequential order. This allows parts to be processed one at a time or, in some cases, in a constant small batch that is maintained through the process sequence. The purpose of a cell is to achieve and maintain an efficient, continuous flow of work.

Continuous flow. Each process, whether in an office or plant setting, makes or completes only the one piece that the next process needs; the batch size is one. Single-piece flow, or one-piece flow, is the opposite of a batch-and-queue process.

Cycle time. This is the time a person needs to complete an assigned task or activity before starting again.

DMAIC. This acronym stands for “define, measure, analyze, improve, and control. It is the heart of the Six Sigma process and refers to a data-driven quality strategy for improving processes. It is an integral part of any company’s Six Sigma quality initiatives.

Green Belt. A Green Belt is an employee who has been trained on the Six Sigma improvement methodology and will lead a team. The degree of knowledge and skills associated with Six Sigma is less than that of a Black Belt or Master Black Belt. Extensive product knowledge is a must in a green Belt’s task of process improvement.

Heijunka. This Japanese term refers to the act of leveling the variety or volume of items produced by a specific process over a period of time. This system is used to avoid excessive batching of product types or volume fluctuations, especially with a pacemaker process.

JIT. “JIT” stands for “just in time.” This means producing or conveying only the items that are needed by the next process when they are needed and in the quantity needed. This process can even be used between facilities or companies.

This is a signaling device that gives instructions for production or conveyance of items in a pull system.

“Kaizen” is the Japanese word for improvement. However, it implies more than improvement in the basic production processes. Kaizen represents a philosophy by which an organization and the individuals within it undertake continual improvements in all aspects of organizational life, based on the idea that a process is never perfect.

Lean. This is simply a thought process, not a tool. The key thought processes within Lean are identifying waste from the customer’s perspective and then determining how to eliminate it.

Master Black Belt. These are Six Sigma quality experts who are responsible for strategic implementations within an organization. Their main responsibilities include training and mentoring of Black Belts and Green Belts; helping to prioritize, select, and charter high-impact projects; maintaining the integrity of Six Sigma measurements, improvements, and “tollgates” (control points); and developing, maintaining, and revising Six Sigma training materials.

Material flow. The movement of a physical product through the value stream.

One-piece flow. In its purest form, one-piece flow means that items are processed and moved directly to the next station one piece at a time. Each processing step completes its specific work just before the next process needs the item; the transfer batch is one.

Opportunity cost. This is the foregone value of an alternative that is precluded by choosing another alternative. Other types of costs may include variable, fixed, direct, indirect, period, and product.

Overproduction. This is the process of producing more, sooner, or faster than is required by the next process or customer.

Procedure (Poka Yoke). This is a mistake-proof device or procedure designed to prevent a defect from occurring throughout the system or process.

Productivity. This is the ratio of measured outputs over measured inputs, such as the number of widgets produced per man-hour.

Six Sigma. The Six Sigma process is designed to eliminate variances in a process in order to allow the best flow of work using the necessary analytical tools and processes.

Standard work. This term refers to a precise description of each work activity’s cycle time, “takt time” (see below), sequence of specific tasks, and the minimum inventory of parts needed on hand to conduct the activity.

Supermarket. This is a very visible, controlled inventory of items that is used to schedule production at an upstream process.

Takt time. This is the rate of demand from a customer. Takt time equals the available operating time or requirement.

Theory of constraints. This theory describes the methods used to maximize operating income when an organization is faced with bottleneck operations.

Value. This term refers to a product or service capability that is provided to a customer at the right time and at an appropriate price.

Value stream. This term encompasses all activities, both value added and non-value added, that are required to bring a product, group, or service from the point of order to the hands of a customer and a design from concept to launch to production to delivery.

Value stream mapping. This is a pencil-and-paper tool used to—

  • Follow a product or information (or both) activity path from beginning to end and draw a visual representation of every process—whether value added and non-value added—in the material and information flows.
  • Design a future-state map that has waste removed and creates more flow.
  • Produce a detailed implementation plan for the future state of the organization.

Waste (Muda). Waste includes anything that does not add value to a final product or service, such as an activity that the customer would not want to pay for if it knew it was happening.

Waste types. Sources of waste can include overproduction, excess inventory, defects, overprocessing, unneeded motion, wasted employee talents, waiting, transport delays, and reprioritization actions.

WIP (Work in process). These are items—material or information—that are between machines, processes, or activities waiting to be processed.