A treaty is an agreement under international law entered into by actors in international law, namely sovereign states and international organizations. A treaty may also be known as an (international) agreement, protocol, covenant, convention, pact, or exchange of letters, among other terms. Regardless of terminology, all of these forms of agreements are, under international law, equally considered treaties and the rules are the same. 

Treaties can be loosely compared to contracts: both are means of willing parties assuming obligations among themselves, and a party to either that fails to live up to their obligations can be held liable under international law. 

A treaty is an official, express written agreement that states use to legally bind themselves. A treaty is the official document which expresses that agreement in words; and it is also the objective outcome of a ceremonial occasion which acknowledges the parties and their defined relationships. 

Since the late 19th century, most treaties have followed a fairly consistent format. A treaty typically begins with a preamble describing the contracting parties and their joint objectives in executing the treaty, as well as summarizing any underlying events (such as a war). Modern preambles are sometimes structured as a single very long sentence formatted into multiple paragraphs for readability, in which each of the paragraphs begins with a verb (desiring, recognizing, having, and so on).
Does a treaty hold up in a country other than the one in which it was written?
A treaty is an agreement under international law entered into by actors in international law,