A reservation in international law is a to a state's acceptance of a treaty. A reservation is defined by the 1969 Vienna Convention on the Law of Treaties (VCLT) as:

a unilateral statement, however phrased or named, made by a State, when signing, ratifying, accepting, approving or acceding to a treaty, whereby it purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that State. (Article 2 (1)(d))