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

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

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.

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.

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.

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.

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.

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.

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

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.

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.

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.
Short ton. A unit of weight equal to 2,000 pounds.

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.