Non-tariff barriers in international trade

What does non-tariff barrier mean in international trade?

Contemporary Economic Development Strategies in today’s global business system encourage countries to do more exports and fewer imports to achieve a sustainable development. 

Especially less developed countries that could not reach adequate export levels try to limit their imports in an aggressive ways. 

As tariffs have been decreased by WTO agreements all around the world now the only choice left for these kinds of countries that can be used to restrict the import is Non-tariff barriers (NTB).