The federal agency that administers federal tax laws, assesses and collects taxes, audits taxpayers, and handles appeals by taxpayers who dispute their tax liability. ABBRV. IRS. international agreement.N. An agreement between two or more nations that creates legal rights or obligations among them; a treaty,convention, or other such agreement between nations. International Court of Justice.N. The United Nations' court, seated at The Hague, Netherlands, that provides advice on questions of law...