Constraint
This design strategy limits the actions that a user takes, either through physical constraint or psychological constraints. Physical constraints include paths (like a swipe or scroll), axes (a rotary dial or a trackball) and barriers (the computer screen edges or an electric plug). Constraints are helpful to minimize user’s mistakes and slips by making the error difficult or impossible to make in the first place.
Definition Sources: UPoD and NNG’s “Preventing User Errors: Avoiding Unconscious Slips” by Page Laubheimer (https://www.nngroup.com/articles/slips/)
Source: UPoD
Source: “Taking Donald Norman’s Design Principles to Web Design, Part 2” by Patrick McNeil (http://www.howdesign.com/web-design-resources-technology/donald-normans-design-principles-applied-modern-web-design-part-2/).
Source: Original photo (dishwasher liquid container as example of constraint to prevent user error)
Constraint
I appreciate what you wrote in describing the meaning of constraints. You were able to take something that could potentially be written in a complicated way and simplified it so that many more people could read and understand what a constraint is about.
Besides the physical constraints that you mentioned above, I feel it is also important to speak about the psychological constraints that we have as well. Examples of these can be found in the visual design of interfaces where nomenclature and icons can be used to help a user navigate a mobile app. Another example is when visual design is used to create a perceived relationship between elements of a particular visual graphics.
Design Fundamentals: Constraints
https://www.webdesignerdepot.com/2013/02/design-fundamentals-constraints/