Definitions in this glossary are adapted from the U.S. Department of Transportation, Research and Innovative Technologies Administration, Bureau of Transportation Statistics, available at

All hazards incident. Refers to any incident, the result of terrorism or a natural disaster, that could affect the maritime transportation system.

Ballast water. Fresh or salt water, sometimes containing sediments, held in tanks and cargo holds of ships to increase stability and maneuverability during transit.

Break-bulk. Packages of maritime cargo that are handled individually, palletized, or unitized for purposes of transportation as opposed to bulk and containerized freight.

Bulk carrier. A ship with specialized holds for carrying dry or liquid commodities, such as oil, grain, ore, and coal, in unpackaged bulk form. Bulk carriers may be designed to carry a single bulk product (crude oil tanker) or accommodate several bulk product types (ore/bulk/oil carrier) on the same voyage or on a subsequent voyage after holds are cleaned.

Chained dollars. A measure used to express real prices, defined as prices that are adjusted to remove the effect of changes in the purchasing power of the dollar. Real prices usually reflect buying power relative to a reference year. The "chained-dollar" measure is based on the average weights of goods and services in successive pairs of years. It is "chained" because the second year in each pair, with its weights, becomes the first year of the next pair. Before 1996, real prices were expressed in constant dollars, a weighted measure of goods and services in a single year. See also current dollars.

Class I freight railroad. Defined by the American Association of Railroads each year based on annual operating revenue. For 2008, the threshold for Class I railroads was revenues exceeding $360 million. A railroad is dropped from the Class I list if it fails to meet the annual revenue threshold for three consecutive years.

Container. A large standard-size metal box into which cargo is packed for shipment aboard specially configured oceangoing containerships. It is designed to be moved with common handling equipment to enable high-speed intermodal transfers in economically large units between ships, railcars, truck chassis, and barges using a minimum of labor. Therefore, the container rather than the cargo in it serves as the transfer unit.

Containerization. A system of intermodal freight transportation that uses standard containers that can be loaded onto vessels, railcars, and trucks. It involves the stowage of general or special cargo in a container for transport in the various modes.

Containership. A cargo vessel designed and constructed to transport, within specifically designed cells, portable tanks and freight containers, which are lifted on and off with their contents intact.

Containerized cargo: Cargo that is practical to transport in a container and results in a more economical shipment than could be achieved by shipping the cargo in some other form of unitization (e.g., break-bulk).

Container terminal. An area designated for the stowage of cargo in containers. It is usually accessible by truck, railroad, and marine transportation. At a container terminal, containers are picked up, dropped off, maintained, and housed.

Container throughput. A measure of the number of containers handled over a period of time. It is a standard measure for the productivity of a seaport. Container throughput is measured by twenty-foot equivalent units (TEU).

Current dollars. Dollar value of a good or service in terms of prices current at the time the good or service is sold. See also chained dollars.

Customs-Trade Partnership Against Terrorism (C-TPAT). A voluntary public-private partnership program in which the private owners of supply chain infrastructure and cargo work with U.S. Customs and Border Protection to improve the security of the international supply chain. See for details.

Deadweight tons (dwt). The total weight of a ship's load, including cargo, fuel, and crew. The deadweight tonnage of a ship is the difference between its weight when completely empty and its weight when fully loaded.

Gross domestic product (GDP). The total value of goods and services produced by labor and property located in the United States. As long as the labor and property are located in the United States, the supplier (the workers and, for property, the owners) may be either U.S. residents or residents of foreign countries.

Highway-rail crossing. A location where one or more railroad tracks intersect a public or private thoroughfare, a sidewalk, or a pathway.

Intermodal container. A freight container designed to permit it to be used interchangeably in two or more modes of transport.

Intermodal. Used to denote movements of cargo containers interchangeably between transport modes-i.e., motor, water, and air carriers-and where the equipment is compatible within the multiple systems.

Just in time (JIT). A method of inventory control in which warehousing is minimal or nonexistent. A container is the movable warehouse and must arrive "just in time," not too early or too late.

Marine terminal. A designated area of a port used for the transmission, care, and convenience of cargo and/or passengers in the interchange of them between land and water carriers or between two water carriers. It includes wharves, warehouses, covered and/or open storage spaces, cold storage plants, grain elevators and/or bulk cargo loading and/or unloading structures, landings, and receiving stations.

Marine Transportation System (MTS). Consists of all the intermodal components that are part of the maritime domain, including ships, ports, inland waterways, intermodal rail and truck, and other users of the maritime system.

Merchandise trade exports. Merchandise transported out of the United States to foreign countries whether such merchandise is exported from within the U.S. Customs Service territory, from a U.S. Customs bonded warehouse, or from a U.S. Foreign Trade Zone. (Foreign Trade Zones are areas, operated as public utilities, under the control of U.S. Customs with facilities for handling, storing, manipulating, manufacturing, and exhibiting goods.)

Merchandise trade imports. Commodities of foreign origin entering the United States, as well as goods of domestic origin returned to the United States with no change in condition or after having been processed and/or assembled in other countries. Puerto Rico is a customs district within the U.S. Customs territory, and its trade with foreign countries is included in U.S. import statistics. U.S. import statistics also include merchandise trade between the U.S. Virgin Islands and foreign countries even though the islands are not officially a part of the U.S. Customs territory.

Port. A harbor area in which marine terminal facilities for transferring cargo between ships and land transportation are located.

Real gross domestic product (GDP). The real counterpart to current/nominal GDP, obtained by valuing output in a given year at prices from another year, called the base year. It reflects correction for inflation and changes in the price of goods and services.

Roll-on/roll-off vessel. Ships that are designed to carry wheeled containers or other wheeled cargo and that use the roll-on/roll-off method for loading and unloading.

Secure Freight Initiative (SFI). A joint program of the U.S. Department of Homeland Security and the U.S. Department of Energy that is designed to scan U.S.-bound containers for nuclear or radiological materials at their foreign ports of origin. See for details.

Tanker. An oceangoing ship designed to haul liquid bulk cargo in world trade.

Twenty-foot equivalent unit (TEU). The standard unit for measuring the volume of containers that seaports handle. Standard container sizes are 20 feet, 40 feet, and 48 feet long.

Virtual container yard. Virtual container yards are Web-based platforms where users can match empty containers to container needs at the dock rather than returning them to the terminal.