What is a tariff?

Originally a tariff is a charge made for goods or services. If an item or service costs X dollars, then that is the tariff.
However, language and words are dynamic and are often used to mean something other than their original meaning.
When that new meaning is accepted then the word changes its definition.
Tariff is now a tax. Additional payment over and above the value of the goods or services.
Tariff is often used by governments on imported goods, an additional tax to increase the price of those goods to give domestic or home manufactured goods an advantage.
A tariff is a tax that is placed on an imported good.

A tariff is a tax on an imported good. Therefore for each unit of a good that is imported into a country the tariff increases the price of that good by however much the tariff is.

Tariffs are usually implemented when the world price of a good is lower than the domestic price of a good. A tariff thus is a form of protection from foreign competition that can produce that good at a cheaper price. The jobs of that industry are thus protected by the tariff, as opposed to the jobs being eliminated by foreign competition. This makes consumers outside the industry lose because they have to pay a higher price for that good.

Tariffs are a tax on importation, when you import a product over to a different country you have to pay a Tariff which is also known as a Tax when it first arrives in the country. Tariffs make the product your importing more expensive. The Company pays for the Tariff.
A tax on imports and exports.
The official definitions of the word tariffs are "a tax or duty to be paid on a particular class of imports or exports."
A tax imposed on imported goods and services. Tariffs are used to restrict trade, as they increase the price of imported goods and services, making them more expensive to consumers.