Customs is the plural of custom, a common practice among a group of people.
Customs duty is a tariff or tax on the import or export of goods. Traditionally in England, it was part of the customary revenue of the king, and therefore did not need parliamentary consent to be levied, unlike excise duty, land tax, or other impositions.
So Customs is an authority or agency in a country responsible for collecting customs duty and for controlling the flow of people, animals and goods, as well as personal effects and hazardous items, in and out of the country. Depending on local legislation and regulations, exporting or importing of some goods may be restricted or forbidden, and the Customs agency enforces these rules. The customs agency is different from the immigration authority, which monitors persons who leave or enter the country, checking for appropriate documentation, apprehending people wanted by international search warrants, and impeding the entry of others deemed dangerous to the country.
