International organisation

Definition in the Law art. 4

an organisation and its subordinate bodies governed by public international law, or any other body which is set up by, or on the basis of, an agreement between two or more states.

In plain words

An international organisation is an organisation and its subordinate bodies governed by public international law, or any other body set up by, or on the basis of, an agreement between two or more states. For example, the definition matters to a company that sends data to such an organisation.