Abbreviated "MFN", it's the clause in an international trade agreement that grants signatory countries the same tariff rate
In international trade, the term most-favored-nation (MFN) treatment has a 
meaning at ... MFN clause, and be in compliance with the criteria of the ... Trade 
agreements with NME countries must be approved by joint resolution, .... 
concessional rates (often referred to as MFN rates, and listed in the U.S. tariff.