Nature of duties or the duty nature refer to the different kinds of customs duty.  The duty nature can be an ad valorem, specific, compound, mixed, variable, "tariffied" or unclassified duty.

A nomenclature is an agreed system for classifying goods according to defined criteria, and in given detail and order, by associating to product groups a number which is used by all parties which adopt the nomenclature.

 

The measurement of the nominal tariff protection relates the duty to the value of the imported product as opposed to the effective protection which relates the duty to the value added in manufacturing the product. 

Measures other than tariffs which restrict imports or exports, such as quotas, import licensing systems, sanitary regulations, prohibitions, etc. Also known as non-tariff barriers.