a. Treaty is 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. (Article 2 of The Vienna Convention on the Law of Treaties, VCLT, 1969).

b. Treaty is an agreement formally signed, ratified, or adhered to between two nations or sovereigns; an international agreement concluded between two or more states in written form and governed by international law. (Black's Law Dictionary - 9th edition).

c. Treaty is a formally concluded and ratified agreement between States. The term is used generically to refer to instruments binding at international law, concluded between international entities (States or organizations). Under the Vienna Conventions on the Law of Treaties, a treaty must be: (1) a binding instrument, which means that the contracting parties intended to create legal rights and duties; (2) concluded by states or international organizations with treaty-making power; (3) governed by international law and (4) in writing. (UN Treaty Collection – Definition of Key Terms)

d. Treaty is a formal agreement between two states signed by official representatives of each state. (Duhaime's Law Dictionary)

a. Agreement is a mutual understanding between two or more persons about their relative rights and duties regarding past or future performances; a manifestation of mutual assent by two or more persons. (Black's Law Dictionary - 9th edition).

b. Agreement is the parties' actual bargain as found in their language or by implication from other circumstances, including course of dealing, usage of trade, and course of performance. (Black's Law Dictionary - 9th edition)..

a. Pact is an agreement between two or more parties; esp., an agreement (such as a treaty) between two or more nations or governmental entities. (Black's Law Dictionary - 9th edition).

a. Accord is an amicable arrangement between parties, esp. between peoples or nations. (Black's Law Dictionary - 9th edition).

b. Accord is an offer to give or to accept a stipulated performance in the future to satisfy an obligor's existing duty, together with an acceptance of that offer. (Black's Law Dictionary - 9th edition).

a. Convention is an agreement or compact, esp. one among nations; a multilateral treaty. (Black's Law Dictionary - 9th edition).

b. Convention is a formal agreement between States. The generic term ‘convention’ is thus synonymous with the generic term ‘treaty’. Conventions are normally open for participation by the international community as a whole, or by a large number of States. Usually the instruments negotiated under the auspices of an international organization are entitled conventions. (UN Treaty Collection – Definition of Key Terms)

a. Covenant is a formal agreement or promise, usu. in a contract or deed, to do or not do a particular act. (Black's Law Dictionary - 9th edition).

b. Covenant is a written document in which signatories either commit themselves to do a certain thing, to not do a certain thing or in which they agree on a certain set of facts. (Duhaime's Law Dictionary)

a. Declaration is a formal statement, proclamation, or announcement, esp. one embodied in an instrument. (Black's Law Dictionary - 9th edition).

b. Declaration is used for various international instruments. International human rights declarations are not legally binding; the term is often deliberately chosen to indicate that the parties do not intend to create binding obligations but merely want to declare certain aspirations. However, while the 1948 Universal Declaration of Human Rights for example was not originally intended to have binding force, its provisions have since gained binding character as customary law. (UN Treaty Collection – Definition of Key Terms)

a. Memorandum of Understanding is document intended to become a contract but which, if meeting other criteria, can be recognized, in law, as a contract. (Duhaime's Law Dictionary)

a. Charter is an instrument that establishes a body politic or other organization, or that grants rights, liberties, or powers to its citizens or members. (Black's Law Dictionary - 9th edition).

b. Charter is an instrument by which a municipality is incorporated, specifying its organizational structure and its highest laws; specif., a written document making the persons residing within a fixed boundary, along with their successors, a corporation and body politic for and within that boundary, and prescribing the powers, privileges, and duties of the corporation. (Black's Law Dictionary - 9th edition).

c. Charter is used for particularly formal and solemn instruments, such as the treaty founding an international organization like the United Nations. (UN Treaty Collection – Definition of Key Terms)

a. Statute is a law passed by a legislative body; specif., legislation enacted by any lawmaking body, including legislatures, administrative boards, and municipal courts. (Black's Law Dictionary - 9th edition).

b. Statute is the written law approved by legislatures, parliaments or elected or appointed houses of assembly. (Duhaime's Law Dictionary)

a. Constitution is a The fundamental and organic law of a nation or state that establishes the institutions and apparatus of government, defines the scope of governmental sovereign powers, and guarantees individual civil rights and civil liberties. (Black's Law Dictionary - 9th edition).

b. Constitution is the written instrument embodying this fundamental law, together with any formal amendments. (Black's Law Dictionary - 9th edition).

c. Constitution is the basic, fundamental law of a state which sets out how that state will be organized and the powers and authorities of government between different political units and citizens. (Duhaime's Law Dictionary)

a. Principles are fundamental truth or doctrine, as of law; a comprehensive rule or doctrine which furnishes a basis or origin for others; a settled rule of action, procedure, or legal determination. A truth or proposition so clear that it cannot be proved or contradicted unless by a proposition which is still clearer. That which constitutes the essence of a body or its constituent parts. That which pertains to the theoretical part of a science. (Black's Law Dictionary - 6th edition-1990).

a. Protocol is a summary of a document or treaty. (Black's Law Dictionary - 9th edition).

b. Protocol is a treaty amending and supplementing another treaty. (Black's Law Dictionary - 9th edition).

c. Protocol is an international agreement of a less formal nature than a treaty and which amends, supplements or clarifies a treaty. (Duhaime's Law Dictionary)

a. Optional Protocol is used for additional legal instruments that complement and add to a treaty. A protocol may be on any topic relevant to the original treaty and is used either to further address something in the original treaty, address a new or emerging concern or add a procedure for the operation and enforcement of the treaty—such as adding an individual complaints procedure. A protocol is ‘optional’ because it is not automatically binding on States that have already ratified the original treaty; States must independently ratify or accede to a protocol. (UN Treaty Collection – Definition of Key Terms)

a. Exchange of Letters : States may express their consent to be bound by an "exchange of letters/notes". The basic characteristic of this procedure is that the signatures do appear not on one letter or note but on two separate letters or notes. The agreement therefore lies in the exchange of both letters or notes, each of the parties having in their possession one letter or note signed by the representative of the other party. In practice, the second letter or note, usually the letter or note in response will typically reproduce the text of the first. In a bilateral treaty, letters or notes may also be exchanged to indicate that all necessary domestic procedures have been completed.

b. An "exchange of notes" is a record of a routine agreement that has many similarities with the private law contract. The agreement consists of the exchange of two documents, each of the parties being in the possession of the one signed by the representative of the other. Under the usual procedure, the accepting State repeats the text of the offering State to record its assent. The signatories of the letters may be government Ministers, diplomats or departmental heads. The technique of exchange of notes is frequently resorted to, either because of its speedy procedure, or, sometimes, to avoid the process of legislative approval. ( United Nations Treaty Collection )

a. Armistice is a suspending or cessation of hostilities between belligerent nations or forces for a considerable time. An armistice differs from a mere "suspension of arms" (q. v.) in that the latter is concluded for very brief periods and for local military purposes only, whereas an armistice not only covers a longer period, but is agreed upon for political purposes. It is said to be general if it relates to the whole area of the war, and partial if it relates to only a portion of that area. (Black's Law Dictionary - 6th edition 1990).

b. Armistice is an agreement concluded between two or more States waging war against each other. The expression is not used in non-international armed conflicts. The purport of an armistice agreement has undergone a radical change in the last century. Until the World Wars, an armistice meant an agreement designed to bring about a mere suspension of hostilities between belligerent parties who remained locked in a state of war with each other, and the expression was synonymous with truce. (Public International Law, Oxford)

a. Statement is an allegation; a declaration of matters of fact. The term has come to be used of a variety of formal narratives of facts, required by law in various jurisdictions as the foundation of judicial or official proceedings and in a limited sense is a formal, exact, detailed presentation. (Black's Law Dictionary - 6th edition 1990).

a. Travaux Preparatoires [French "preparatory works"] is a material used in preparing the ultimate form of an agreement or statute, and esp. of an international treaty; the draft or legislative history of a treaty. (Black's Law Dictionary - 9th edition).