An intermodal container (also container, freight container, ISO container , shipping container, hi-cube container, box, conex box and sea can) is a standarized reusable steel box used for the safe, efficient and secure storage and movement of materials and products within a global containerized intermodal freight transport system. Lengths of containers, which each have a unique ISO 6346 reporting mark, vary from 8-foot (2.438 m) to 56-foot (17.07 m) and heights from 8-foot (2.438 m) to 9 feet 6 inches (2.9 m). There are approximately seventeen million intermodal containers in the world of varying types to suit different cargoes.[1] Aggregate container capacity is often expressed in twenty-foot equivalent units (TEU / teu) which is a unit of capacity equal to one standard 20 × 8 ft (6.10 × 2.44 m) (length × width) container.