Article 2(1)(a) VCLT defines 'TREATY' as:

1. Article 2(1)(a) VCLT defines 'treaty': 'an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation'. 2. Three key elements: (i) BETWEEN STATES; (ii) WRITTEN FORM; (iii) governed by INTERNATIONAL LAW. 3. Treaties with international organisations are governed by the 1986 Vienna Convention. 4. Designations vary: treaty, convention, protocol, charter, statute, pact, agreement, accord — all are 'treaties' if they satisfy these elements. 5. Hence option B is correct. _Source: UN Charter 1945 / Vienna Convention on Law of Treaties 1969 / ICJ Statute / ARSIWA 2001 — Vienna Convention on the Law of Treaties 1969, Article 2(1)(a)_