What is Proportionality?

Legal Definition
Proportionality is a general principle in law which covers several special (although related) concepts. The concept of proportionality is used as a criterion of fairness and justice in statutory interpretation processes, especially in constitutional law, as a logical method intended to assist in discerning the correct balance between the restriction imposed by a corrective measure and the severity of the nature of the prohibited act. Within criminal law, it is used to convey the idea that the punishment of an offender should fit the crime. Under international humanitarian law governing the legal use of force in an armed conflict, proportionality and distinction are important factors in assessing military necessity.
-- Wikipedia