Customary International Law
International laws that derive their authority from the constant and consistent practice of States, rather than from formal expression in a treaty or legal text. In order for State practice to contribute to the formation of customary international law, that practice should be conducted with a sense of legal obligation. Several of the provisions in the Universal Declaration of Human Rights, including the prohibition against slavery, torture, prolonged arbitrary detention and extra-judicial killings, are generally recognized to have become part of customary international law.
UN High Commissioner for Refugees, UNHCR Master Glossary of Terms, June 2006, Rev.1,
available at: http://www.refworld.org/docid/42ce7d444.html