constraint

Something that constrains; a restriction.

An engineer must recognize the difference between a constraint (to work within) and a problem (to be eliminated via resolution).

Today’s electricity demand (65 EJ/a) is well covered by the range, but constraints may occur in the long run locally. Amongst large countries, Nigeria and India may need imports to meet electricity demand.

An irresistible force or compulsion.

They confessed, but only under severe constraint.

The repression of one's feelings.

Although his blood so rose against this man, and his wrath so stirred within him, that he could have struck him dead, he put such fierce constraint upon himself that he passed him without a word or look. Yes, and he would have gone on, and not turned, though to resist the Devil who poured such hot temptation in his brain, required an effort scarcely to be achieved, if this man had not himself summoned him to stop

A condition that a solution to an optimization problem must satisfy.

A linkage or other restriction that maintains database integrity.