A more thorough explanation:

A peremptory norm, also known as jus cogens, is a rule of international law that is considered to be of utmost importance and cannot be violated or modified by any other law or agreement. It is a norm that has been accepted and recognized by the international community of states of the United Nations.

For example, the prohibition of genocide, slavery, and torture are considered peremptory norms. These norms are so fundamental that they are considered to be part of customary international law, which means that they are binding on all states, regardless of whether they have ratified any treaties or agreements.

If a treaty or agreement conflicts with a peremptory norm, it is considered to be void and has no legal effect. This means that states cannot use treaties or agreements to justify actions that violate peremptory norms.

Overall, peremptory norms are essential for maintaining the integrity and stability of the international legal system. They ensure that certain fundamental values and principles are respected and upheld by all states.