In the parlance of design, a constraint is any construct that either inhibits or prohibits certain activity within a given context. Constraints also exist within the process of design itself, such as those of resources like time and money, which often dictate the course of action.

The complement of a constraint is called an affordance.

Pencil sketch of a desert highway with a speed limit sign, a double line and an oncoming truck depicted as constraints, and the way forward as an affordance.

A practical example of a constraints and affordances is this: on a highway, medians and painted lines are constraints and the paving and direction of the road are affordances.