Glossary

New to systems science? These are the foundational concepts — the shared language for analyzing any complex system.

The Basics

System
An organized set of interacting components forming a coherent whole, with identifiable boundaries separating it from its environment.
Boundary
The demarcation separating a system from its environment, including the interfaces where exchanges occur. Controls what flows in and out.
Environment
Everything outside the system boundary — the sources providing inputs, the sinks receiving outputs, and the channels through which flows occur.

The Parts

Component
A distinct part within a system that performs specific functions and interacts with other components through defined interfaces.
Subsystem
A component inside a system that is itself a system — with its own boundaries, components, and behaviors. Systems nest within systems.
Interface
A connection point where a system meets its environment or where components connect to each other. Where exchanges happen.

The Dynamics

Flow
The movement of matter, energy, or messages between components or across boundaries. The substance transfers that keep systems functioning.
State
The configuration of a system at a specific moment — the values of its variables and relationships between components right now.
Feedback Loop
A circular process where a system's output returns to influence its input. Can amplify (positive) or stabilize (negative) system behavior.
Adaptation
How a system modifies itself in response to changes — adjusting structure or behavior to maintain functionality or improve fitness.

The Patterns

Structure
The arrangement and relationships between components — how the system is organized. Structure enables and constrains what the system can do.
Function
What a system or component does — its role, purpose, or activity. Different structures can perform the same function.
Emergence
When complex patterns or behaviors arise from simpler component interactions — properties the whole has that the parts don't have alone.

Go deeper

Explore 135+ interconnected notes on systems thinking, complexity, and the patterns that connect in the Halcyonic Garden — a digital garden of ideas from Bateson, Bunge, and beyond.

Apply it

Want to see these concepts in practice? BERT is an open-source toolkit for applying rigorous systems analysis to any domain.