Containers are reusable storage units used by the cargo industry to store, protect and transport raw materials, manufactured goods and other goods between the seaports of different countries. First appearing in the 1950s, they are usually rectangular and primarily made of metal or fibreglass. Their design means they can carry heavy loads, be placed on top of each other into space-saving stacks on ships and in ports and resist the harsh environment of ocean voyages. The use of containers allows individual items or packages to be grouped into a single larger unit load. This reduces cargo handling which improves security, allows faster freight transport and reduces damage and losses. The use of standard container sizes simplifies movement, handling and port facilities by allowing common facilities, technology and equipment. It also means that shipping containers can be intermodal (be used by more than one mode of transport).
Shipping containers typically exist in 20 foot and 40 foot lengths. The standard measure of containers in international trade is the twenty foot equivalent (TEU) which is the space occupied by a standard 20 foot container. Different types of containers are available depending upon the type of freight to be moved (e.g. refrigerated, liquid, insulated, flat and ventilated). Specialised or customised containers can be used for sensitive, fragile, dangerous or confidential items.