A container is a sealed, rigid, reusable metal box used to convey products by vessel, truck, or rail. The container must be designed for repeated use, be simple to fill and empty, and be specifically designated to allow for the carriage of goods without the need for intermediate reloading. All containers must have construction fittings that can sustain the transport pressure that may be applied in some instances during regular continuous transportation use.

Furthermore, shipping containers range in size from massive reusable steel boxes used for intermodal transport to more ordinary corrugated boxes. The terms "container" or "shipping container" are nearly synonymous in the context of international shipping trade with "intermodal freight container", a container designed to be transported from one mode of transport to another without unloading and reloading.

Freight containers are reusable transport and storage units used to transfer goods and raw materials between cities or nations. According to Wikipedia, there are over seventeen million intermodal containers in the globe, and shipping containers convey a significant amount of the world's long-distance freight generated by international trade. The creation of these containers contributed significantly to the globalization of commerce in the second half of the twentieth century, greatly lowering the cost of shipping goods and hence long-distance trade.

High cube containers (which provide an extra 1 ft (305 mm) of height to normal shipping containers), pallet wides, open tops, side loaders, double door or tunnel-tainers, and temperature controlled containers are examples of specialized shipping containers. A portable fuel and oil freight container, known as a Transtainer, is another specialty container. The hybrid bulk fuel tank was designed with the construction, mining, logging, and farming industries in mind. The tank can transport and store hazardous liquids as well as bulk fuels via road, rail, and sea.