A treaty is an agreement uner international law entered into by actors in international law, namely states and international organizations. A Treaty may also be known as: (international) agreement, protocol, covenant, convention, exchange of letters, accord, exchange of notes, memorandum of understanding, etc. Regardless of the terminology, all of these international agreements under international law are equally treaties and the rules are the same. (Note that in United States constitutional law, the term "treaty" has a special meaning which is more restricted than its meaning in international law; see below.)