A more thorough explanation:

Definition: Customary international law refers to international obligations that arise from established international practices, rather than from formal written conventions and treaties. It results from a general and consistent practice of states that they follow from a sense of legal obligation.

Examples:

• The doctrine of non-refoulement: This is a principle of international law that prohibits the expulsion, deportation, or return of a person to a country where they may face persecution or harm. It is a customary international law that has been recognized by many countries and international organizations.
• The granting of immunity for visiting heads of state: This is a customary international law that provides immunity to visiting heads of state from criminal prosecution or civil lawsuits in the host country. This law is based on the principle of sovereign equality of states and is recognized by most countries.

Explanation: Customary international law is established by showing state practice and opinio juris. State practice refers to the consistent behavior of states in a particular area of international law, while opinio juris refers to the belief of states that such behavior is legally required. The examples of non-refoulement and immunity for visiting heads of state illustrate how customary international law is created and recognized by states.