What is the MFN?

Most-favoured-nation (MFN): treating other people equally Under the WTO agreements, countries cannot normally discriminate between their trading partners.

MFN means that, in the absence of a trade agreement, you cannot treat one country different to the others. If you decide, for example, to reduce the tariffs for goods from EU, unless you have a trade deal with the EU, then you have to reduce the tariffs for all WTO members. Equally you cannot have a special procedure (such as TSP) with one member unless you make it available to all (unless that special procedure was part of a trade deal).