What is a formal agreement between two or more sovereign states called?

A formal agreement between two or more sovereign states is called a treaty. This term specifically denotes a legally binding agreement that is established and recognized under international law. Treaties typically require ratification by the governing bodies of the states involved, often reflecting a commitment to certain obligations or understandings that have been negotiated.

While "convention," "pact," and "accord" may also refer to agreements or arrangements between states, they do not carry the same legal weight as treaties. A treaty usually entails a more formal and structured process for creation and approval, which is governed by international law. This makes treaties the standard term used in diplomatic relations for binding agreements. Thus, the understanding of a treaty as a formal agreement underscores its significance in ensuring international cooperation and adherence to agreed-upon terms.