S Chart (Sample Standard Deviation Chart)

A control chart used to monitor the variability of a process by plotting the sample standard deviation over time. It complements the X̄ (mean) chart by indicating if the spread of the process variation remains in control.
See also: Control Charts, Statistical Process Control (SPC)

SMED (Single Minute Exchange of Die)

A methodology designed to reduce setup and changeover times in manufacturing processes. Its goal is to shift from changeovers measured in hours to those completed in single-digit minutes, thereby increasing overall equipment efficiency.
Note: “SMED” appears more than once but refers to the same concept.

SPC (Statistical Process Control)

A method that applies statistical techniques to monitor and control a process. SPC uses various control charts (like X̄, R, and S charts) to detect unusual variations and ensure that the process remains stable over time.
See also: S Chart, Process Capability

SQL (Statistical Quality Control)

An approach that employs statistical methods to measure, control, and improve quality throughout production. Although sometimes abbreviated as SQC, when listed as SQL here, it emphasizes data-driven quality control techniques.
See also: SPC, Quality Control

SR (Supplier Rating)

A measure or scoring system used to evaluate and compare suppliers based on criteria such as quality, delivery performance, cost, and service. It helps organizations ensure that their supply chain partners meet established standards.
See also: Supplier Performance Evaluation

Safety

Refers to conditions and practices that protect people, assets, and the environment from harm or accidents. In a business context, it encompasses policies, training, and equipment designed to minimize risk.
See also: Occupational Health, Risk Management

Safety Stock

An additional quantity of inventory held to mitigate the risk of stockouts caused by demand or supply variability. It serves as a buffer to ensure customer service levels during unexpected fluctuations.
See also: Inventory Management, Buffer Stock

Satisfier

A product or service characteristic that fulfills customer requirements. While necessary to meet expectations, a satisfier typically does not create a competitive advantage because customers assume these requirements will be met.
See also: Delighters, Must-Haves

Scatter Diagram / Scatter Plot

A graphical representation used to explore the potential relationship between two quantitative variables. Each point on the chart represents a paired observation, which can help detect correlations or patterns.
See also: Regression Analysis, Correlation

Scientific Management

A theory of management developed by Frederick Taylor that emphasizes the optimization of work processes through time studies, standardization, and a focus on efficiency.
See also: Time and Motion Studies, Process Improvement

Scope Creep

The uncontrolled or unapproved expansion of a project's scope after its initiation. It can lead to delays, cost overruns, and resource strain if not properly managed.
See also: Project Management, Change Control

Seiri (Sort)

A principle from the 5S methodology that involves separating necessary items from unnecessary ones. The goal is to remove or dispose of what is not needed in the workplace, thereby reducing clutter and freeing up space.
See also: 5S System, Workplace Organization

Seiso (Shine)

Another element of the 5S system focused on cleaning and inspecting the workplace. Regular cleaning helps identify issues and maintains a safe, efficient environment.
See also: Workplace Maintenance, Visual Management

Seiketsu (Standardize)

A 5S principle that involves establishing standardized procedures and schedules for maintaining the organization and cleanliness achieved through Seiri and Seiso.
See also: Standard Operating Procedures (SOPs), Consistency

Seiton (Set in Order)

Within the 5S framework, it refers to organizing and arranging tools and materials so that work can proceed efficiently with minimal wasted effort in searching for items.
See also: Visual Management, Workplace Organization

Self-Directed Work Team (SDWT)

A group of employees empowered to manage their own tasks and make decisions with minimal supervision. These teams are responsible for planning, executing, and monitoring their work, which fosters higher engagement and ownership.
See also: Team Autonomy, Cross-Functional Teams

Senge’s Five Disciplines

Concepts introduced by Peter Senge outlining the key components of a learning organization. The disciplines include:

• Personal Mastery
• Mental Models
• Shared Vision
• Team Learning
• Systems Thinking
  See also: Organizational Learning, Continuous Improvement

Sensitivity Analysis

A technique used to determine how different input variables impact a given output within a model. It helps assess uncertainty and the robustness of decisions or predictions by gauging the effect of changes in input values.
See also: Risk Analysis, Scenario Planning

Sequential Sampling

A sampling method that evaluates items one by one (or in small groups) until a decision (acceptance or rejection of a lot) can be made. It often results in fewer overall samples compared with fixed-sample-size plans.
See also: Acceptance Sampling, Quality Control

Shadow Board

A visual organization tool where outlines or “shadows” mark the designated place for each tool or piece of equipment. This promotes consistency and efficiency in tool storage and retrieval.
See also: 5S, Visual Management

Shainin System

A problem-solving and quality improvement methodology developed by Dorian Shainin. It emphasizes rigorous testing and analysis to isolate the root causes of defects, often using comparative experiments.
See also: Root Cause Analysis, Robust Design

Shingo Prize

An award presented to companies that achieve operational excellence through lean practices. Named after Shigeo Shingo, it recognizes organizations with exceptional performance improvements and lean transformation.
See also: Lean Manufacturing, Operational Excellence

Sigma Level

A metric used in Six Sigma that indicates the capability of a process by measuring the distance (in standard deviations) between the process mean and the nearest specification limit. Higher sigma levels denote fewer expected defects.
See also: Process Capability, Six Sigma

Sigma (σ)

A statistical measure of process variability or spread. In quality management, sigma (σ) helps quantify how much a set of values diverges from the mean value.
See also: Standard Deviation, Process Variation

Significance Level (α)

In hypothesis testing, it is the probability threshold below which the null hypothesis is rejected. Commonly set at 0.05, it represents the risk of committing a Type I error (false positive).
See also: Statistical Hypothesis Testing, p-value

Single Sampling

A quality control method where one sample is taken from a lot to determine whether that lot meets predefined quality criteria.
See also: Single Sampling Plan, Acceptance Sampling

Single Sampling Plan

A specific acceptance sampling plan in which a predetermined number of units are sampled, and the lot is accepted or rejected based on the number of defects found.
See also: Quality Inspection, Sampling Methods

Single-Piece Flow

A lean manufacturing principle where items move one at a time through the production process. This minimizes work-in-process inventory and shortens production lead times while improving quality.
See also: Continuous Flow, Lean Production

SIPOC Diagram

A high-level process mapping tool representing:

• Suppliers
• Inputs
• Process
• Outputs
• Customers

It provides an overview of a process’s key elements and helps in scoping process improvement projects.
See also: Process Mapping, Value Stream Mapping

Six Sigma

A data-driven methodology aimed at reducing process variation and defects to achieve near-perfect quality (3.4 defects per million opportunities). It uses statistical tools and structured improvement frameworks.
See also: DMAIC, Process Improvement

Six Sigma Black Belt

A professional certified in Six Sigma methodologies who leads process improvement projects. Black Belts are experts in statistical analysis and problem-solving techniques and typically work full-time on improvement initiatives.
See also: Six Sigma Green Belt, Master Black Belt

Six Sigma Green Belt

An individual with intermediate training in Six Sigma who supports improvement projects, often while performing regular job functions. Green Belts typically analyze data and implement solutions under the guidance of Black Belts.
See also: Six Sigma, Process Improvement

Six Sigma Master Black Belt

An expert in Six Sigma with advanced knowledge and experience. Master Black Belts mentor Black and Green Belts, lead strategic projects, and are responsible for the organization-wide deployment of Six Sigma principles.
See also: Six Sigma Leadership, Process Optimization

Six Sigma tools

A collection of statistical, analytical, and process-management tools used to reduce defects, minimize variation, and improve processes. Common Six Sigma tools include control charts, process mapping, root cause analysis, and hypothesis testing.
See also: DMAIC, Statistical Process Control (SPC)

Skurich’s Method

A structured approach for process evaluation and improvement, involving systematic review of performance data and root cause identification to isolate issues and quantify potential improvements.
See also: Root Cause Analysis, Process Improvement
(Note: This method is not widely referenced in mainstream Six Sigma literature.)

Skip-Lot Sampling

An acceptance sampling technique where not every lot is inspected. When quality is consistently high, some lots are “skipped” from inspection, reducing inspection effort while maintaining quality assurance.
See also: Acceptance Sampling, Sampling Plans

SMART Matrix

A project evaluation tool that uses the SMART criteria—Specific, Measurable, Attainable, Relevant, and Time-bound—to define, prioritize, and manage improvement initiatives.
See also: Project Selection, Strategic Planning

SMED (Single Minute Exchange of Dies)

A lean methodology aimed at reducing equipment changeover times to less than ten minutes. SMED streamlines and standardizes setup steps, increasing flexibility and equipment effectiveness.
See also: Lean Manufacturing, Setup Reduction

SPC (Statistical Process Control)

A method that uses statistical techniques, such as control charts, to monitor and control process performance. SPC distinguishes between common and special causes of variation to maintain process stability.
See also: Control Charts, Process Capability

SQL (Statistical Quality Control)

A set of statistical techniques used to measure, control, and improve quality in production processes. SQL overlaps with SPC and includes both process control and acceptance sampling methods.
See also: Statistical Process Control (SPC), Quality Control

SS (Sum of Squares)

A statistical measure representing the total squared deviation of data points from their mean. It is fundamental in analyses such as variance, regression, and ANOVA.
See also: Variance, Analysis of Variance (ANOVA)

Stakeholder

Any individual, group, or organization with an interest in a project, process, or outcome. Stakeholders include employees, customers, suppliers, investors, and regulators.
See also: Stakeholder Analysis, Project Management

Standard

A defined level of performance, specification, or output that must be met. Standards ensure consistency, compliance, and quality in products and processes.
See also: ISO Standards, Best Practices

Standard Deviation (σ)

A statistical measure that quantifies the amount of variation or dispersion in a set of data values. Standard deviation is central to assessing process performance and sigma levels in Six Sigma.
See also: Sigma Level, Process Variation

Standard Work

A documented best-practice procedure for performing a specific task. Standard work ensures consistency, efficiency, and serves as a baseline for further improvements.
See also: Work Instructions, Process Standardization

Standardization

The process of establishing uniform methods, procedures, or criteria to ensure consistency and repeatability in processes or products.
See also: Standard Work, Best Practices

Starbursting (Brainstorming Technique)

A creative brainstorming method that focuses on generating questions about a central idea rather than immediate answers, helping teams uncover issues and improvement opportunities.
See also: Brainstorming, Root Cause Analysis

Statistical Process Control (SPC)

See: SPC (Statistical Process Control)

Statistical Quality Control (SQC)

See: SQL (Statistical Quality Control)

Statistic

A single numerical value calculated from a sample of data, summarizing one aspect (such as mean or median) of the data for analysis and decision-making.
See also: Statistics, Data Analysis

Statistics

The science of collecting, analyzing, interpreting, and presenting numerical data. In Six Sigma, statistics provide the quantitative basis for understanding variation and validating improvements.
See also: Statistical Analysis, Data-Driven Decision Making

Stem-and-Leaf Plot

A data visualization tool that organizes numerical data by place value, preserving the original data while providing a visual summary of distribution and shape.
See also: Histogram, Data Visualization

Strategic Planning

A systematic process for defining an organization’s direction and allocating resources to pursue its strategy. Strategic planning aligns improvement projects with long-term business goals.
See also: Hoshin Kanri, SWOT Analysis

Stratification

The division of data or process outcomes into subgroups based on common characteristics, helping to identify patterns or sources of variation that may be hidden in aggregate data.
See also: Data Segmentation, Pareto Analysis

Stratified Sampling

A sampling method in which the population is divided into homogeneous subgroups (strata) before samples are taken, ensuring each subgroup is adequately represented.
See also: Sampling Methods, Random Sampling

Sustainability

Conducting operations in a way that meets current needs without compromising future resources or capabilities. In process improvement, sustainability ensures that gains are maintained over time.
See also: Continuous Improvement, Environmental Management

Swarm Intelligence

A problem-solving and optimization concept inspired by the collective behavior of social organisms. Swarm intelligence algorithms simulate decentralized, cooperative problem-solving to find optimal solutions.
See also: Artificial Intelligence, Optimization

SWOT Analysis

A strategic planning tool that evaluates an organization’s Strengths, Weaknesses, Opportunities, and Threats to inform decision-making and improvement initiatives.
See also: Strategic Planning, Risk Assessment

Symptom

An observable indicator or signal of an underlying problem. Symptoms prompt further investigation to identify root causes before implementing corrective actions.
See also: Root Cause Analysis, Problem Solving

System

A set of interrelated components working together toward a common goal. In Six Sigma, a system may refer to a collection of processes, procedures, and resources forming an organization’s quality infrastructure.
See also: Process, System Thinking

System Audit

A formal evaluation of a system, such as a quality management system, to determine compliance with standards and identify areas for improvement.
See also: Audit, Compliance

System Kaizen

A continuous improvement approach targeting the overall system rather than isolated processes, focusing on optimizing interconnected aspects for sustainable improvement.
See also: Kaizen, Continuous Improvement

Systematic Sampling

A sampling technique where elements are selected at fixed, regular intervals from a population, ensuring a spread of data collection across the process or production run.
See also: Sampling Methods, Random Sampling

Systematic Variation

Variation in a process caused by identifiable, non-random factors, such as equipment issues or operator bias, which can be targeted for improvement.
See also: Special Cause Variation, Process Variation