When an individual or an entity imports goods into the United States, they may have to pay import tariffs based on rates in the Tariff Schedule.
Common words used for a tariff are import duty, custom duty, custom tariff, etc. Virtually all goods are listed in the tariff schedule; some of them are rated at 0%, and some of them may be rated at 37.5% at the maximum. There are also some exemptions or reductions on tariffs for the items imported for personal use based on the dollar value limit.
Import tariffs are collected at the border or seaports by the Customs Border Protection Department. Either you or your clearing agent needs to fill out a Bill of Entry and some other forms and also needs to provide some documentation. You can also make a declaration online before the shipment arrives at the border to avoid any delays in clearing at the border.
Clearing the goods at the border and paying duty is the responsibility of the importer or his/her appointed agent. You might have seen at the Fedex or similar courier companies asking you to pay the duty when delivering the goods at your door, before they hand over the goods to you. In such cases, Fedex or a similar courier company works as your clearing agent to pay the duty at the border on your behalf and collect the same from you when delivering the goods.