The Chinese word 海关 (hǎiguān), meaning "customs" in the sense of a border control agency for goods and passengers, is a compound noun formed by combining two meaningful characters: 海 (hǎi), meaning "sea" or "ocean", and 关 (guān), meaning "gate", "pass", or "frontier checkpoint". Historically, the term originated from the concept of a coastal checkpoint or "sea gate", as China's traditional points of entry and critical controls for international trade were primarily at its seaports. Over time, the meaning expanded from its literal maritime association to encompass all official border control points, whether by sea, land, or air, that regulate the flow of goods, people, and conveyances in and out of the country, thus forming the modern institutional concept of a customs authority.