The document discusses different types of tariffs. It defines a tariff as a tax or duty levied on goods when they enter or leave a country. Tariffs can be classified in several ways: by purpose (such as revenue tariffs to generate income or protective tariffs to encourage domestic industries), by application between countries (single-column, double-column, or triple-column tariffs), or by quantification method (specific duty as a fixed amount per unit, ad-valorem duty as a percentage of value, compound duty combining the two, or sliding-scale duty varying with price).