There are a lot of terms that are specific to Lean and Six Sigma. If you are unsure about the meaning of a term, please feel free to check our Lean and Six Sigma Glossary for a definition. If you do not find the term you are looking for, please contact us. We would be happy to answer your questions, and we may add your term to the glossary in the future.

Proportion defective

Fraction of units with defects; number of defective units divided by the total number of units; translate the decimal figure to a percentage. See also Defects; Defective

Project rationale or “Business Case”

Broad statement defining area of concern or opportunity, including impact/benefit of potential improvements, or risk of not improving a process; links to business strategies, the customer, and/or company values. Provided by business leaders to an improvement team and used to develop problem statement and Project Charter.

Process redesign

Method of restructuring process flow elements eliminating handoffs, rework loops, inspection points, and other non-value-adding activities; typically means “clean slate” design of a business segment and accommodates major changes or yields exponential improvements (similar to reengineering). See also Process Improvement; Reenigneering

Process measures

Measures related to individual steps as well as to the total process; predictors of output measures.

Process map, or flowchart

Graphic display of the process flow that shows all activities, decision points, rework loops, and handoffs.

Process management

Defined and documented processes, monitored on an ongoing basis, which ensure that measures are providing feedback on the flow/ function of a process; key measures include financial, process, people, innovation. See also Control.

Process improvement

Improvement approach focused on incremental changes/solutions to eliminate or reduce defects, costs or cycle time; leaves basic design and assumptions of a process intact. See also Process redesign.

Process design

Creation of an innovative process needed for newly introduced activities, systems, products, or services

Process capability

Determination of whether a process, with normal variation, is capable of meeting customer requirements; measure of the degree a process is/is not meeting customer requirements, compared to the distribution of the process. See also Control; Control Charts.

Problem/Opportunity statement

Description of the symptoms or the “pain” in the process; usually written in noun-verb structure: usually included in a team charter and supported with numbers and more detail once data have been obtained. See also Charter.

Preliminary plan

Used when developing milestones for team activities related to process improvement; includes key tasks, target completion dates, responsibilities, potential problems, obstacles and contingencies, and communication strategies.


The ability of the measurement to measure consistently. This links to the type of scale or detail of your operational definition, but it can have an impact on your sample size, too.


Trial implementation of a solution, on a limited scale, to ensure its effectiveness and test its impact; an experiment verifying a root cause hypothesis.

Plan-Do-Check-Act, or PDCA

Basic model or set of steps in continuous improvement; also referred to as “Shewhart Cycle” or “Deming Cycle.”

Pareto Principle

The 80/20 rule; based on Vilfredo Pareto’s research stating that the vital few (20 percent of causes have a greater impact than the trivial many (80 percent) causes with a lesser impact.

Pareto Chart

Quality tool based on Pareto Principle; uses attribute data with columns arranged in descending order, with highest occurrences (highest bar) shown first; uses a cumulative line to track percentages of each category/bar, which distinguishes the 20 percent of items causing 80 percent of the problem.