Choose the right answer. From the following, select the odd one out:

Concept: The UN Charter establishes six principal organs of the United Nations - the General Assembly, the Security Council, the Secretariat, the Economic and Social Council (ECOSOC), the International Court of Justice (ICJ), and the Trusteeship Council. Separately, the UN system also includes specialized agencies (such as UNESCO, WHO, the IMF, and the World Bank) - autonomous international organizations that cooperate with the UN under formal agreements but were not created as principal organs by the Charter itself.

Application: Among the given options, the Security Council, the General Assembly, and the Secretariat are three of the UN's six principal organs. UNESCO (United Nations Educational, Scientific and Cultural Organization), by contrast, is a specialized agency with its own constitution (adopted in 1945) and independent membership and budget, working in partnership with the UN rather than being one of its principal organs.

Cross-check: The same pattern holds for other well-known specialized agencies, such as WHO, the IMF, the World Bank, and the ILO - none of them are principal organs either, while all three of the other options here fall inside the six-organ set. This confirms UNESCO as the odd one out.