Definition
A constraint is a factor or condition that limits the available courses of action or the ability of a process or system to achieve an objective, performance level or output.
Human Explanation
A constraint defines what cannot be exceeded or what must be taken into account when a system is operated or a decision is made.
Why it Matters
Constraints determine which options are feasible and where improvement can affect the overall result. Ignoring them produces plans that cannot be executed.
Conceptual Boundary
A constraint may be physical, organisational, informational, financial, legal, technical or procedural. It is not automatically a problem or bottleneck; it may be a fixed condition within which a decision must be made.
Practical Perspective
The best solution is often not an unconstrained ideal but the option that best achieves the objective within real conditions. Identify which constraints are binding before adding resources or rejecting an option.