Bound tariffs are the maximum tariffs that can be applied by a WTO member according to its official commitments. They can be very high for some developing countries but are usually not applied. MFN are the tariffs that are legally defined by the country. By definition, they must be below the bound tariffs. The MFN tariffs suffer exceptions, usually because of preferential trade agreements (no tariffs within the EU area, for example) or as special preferences for least developed countries.

Not sure the effectively applied has a legal meaning under WTO.

My bet is that it is a statistical construct: the effective tariff could be a weighted average of tariff duties collected by customs, taking into consideration imports under MFN and imports under preferences. But excluding imports in free zones (export processing industrial parks, for example).

PS (edited). If I may add something on the analytical part. The difference between Bound and MFN tariff duties is called "the tariff water" in the jargon. Some (e.g., at UNCTAD) call it "policy space" because it gives the flexibility to increase applied tariffs up to the limit defined by the international agreement signed by the country. In practice, and up to very recently, rising tariffs was more seen as shooting oneself in the foot than enjoying policy space. But the return of geo-politics and "transactional trade policy" means that raising tariffs or limiting exports of "strategic goods" can be used for geo-political gains, as long as, like the USA or China, you are a big market (nobody would care if Andorra raises its tariffs, except the locals who would have to suffer from increased inflation). Other countries (or regions, as in the case of the EU), use non-tariff measures (norms) to regulate their imports. In the end, it is to be feared that the whole concept of MFN and rules-based trade governance will lose any relevance.

The AHS (Applied Tariff) rate refers to the actual tariff rate that a country imposes on imports, reflecting the rates applied to goods in practice. MFN (Most-Favored-Nation) rate is the lowest tariff rate that a country applies to any WTO member, ensuring equal treatment for all members. The Bound Tariff Rate is the maximum tariff rate a country has agreed to apply under international trade agreements, set during negotiations and legally binding. In tariff analysis, the AHS rate shows the real-world trade conditions, the MFN rate ensures non-discriminatory treatment among WTO members, and the Bound rate limits the extent to which tariffs can be increased.