noun
constraint
kuhn-STRAYNT/kənˈstreɪnt/
A limit on what can happen or be done.
The short tether is a constraint that keeps the dog from reaching the ball.

Etymology
Binding tightly together provides the underlying image: a constraint holds action in check as a bond holds a body. The historical senses of binding and compulsion connect this image to an abstract restriction.
In context
enter FL180 as an altitude constraint, and press INSERT. Now we have a FL180 restriction at the abeam TOID point.
More examples
- Time constraints prevent us from visiting every museum.
- The team designs a new playground within strict budget constraints.
- Reliable transportation removes a major constraint on where she can work.
Forms
constraint · constraints
constrain verb — To limit what someone or something can do.
Similar words
- restriction
- Often suggests an imposed rule rather than a practical obstacle.
- limitation
- Can emphasize limited ability or capacity rather than external conditions.