What is Cargo?

Legal Definition
In economics, cargo or freight are goods or produce being conveyed – generally for commercial gain – by ship, boat, or aircraft, although the term is now often extended to cover all types of freight, including that carried by train, van, truck, or intermodal container. The term cargo is also used in case of goods in the cold-chain, because the perishable inventory is always in transit towards a final end-use, even when it is held in cold storage or other similar climate-controlled facility.

Multi-modal container units, designed as reusable carriers to facilitate unit load handling of the goods contained, are also referred to as cargo, specially by shipping lines and logistics operators. Similarly, aircraft ULD boxes are also documented as cargo, with associated packing list of the items contained within. When empty containers are shipped each unit is documented as a cargo and when goods are stored within, the contents are termed as containerised cargo.
-- Wikipedia
Legal Definition
Mar. law. The entire load of a ship or other vessel. Abb. on Sh. Index, h. t.; 1 Dall. 197; Merl. Rep. h. t.; 2 Gill & John. 136. This term is usually applied to goods only, and does not include human beings. 1 Phill. Ins. 185; 4 Pick. 429. But in a more extensive and less technical sense, it includes persons; thus we say a cargo of emigrants. See 7 Mann. Gr. 729, 744.
-- Bouviers Law Dictionary
Legal Definition
In mercantile law. The load or lading of a vessel; goods and merchandise put on board a ship to be carried in a certain port. The lading or freight of a ship; the goods, merchandise, or whatever is conveyed in a ship or other merchant vessel. Seamans v. Loring, 21 Fed. Cas. 920; Wolcott v. Insurance Co., 4 Pick. (Mass) 429, Macy v. Insurance Co., 9 Mete. (Mass.) 366; Thwing v. Insurance Co.., 103 Mass. 401, 4 Arn. Rep. 567. A cargo is the loading of a ship or other vessel, the bulk of which is to be ascertained from the capacity of the ship or vessel. The word embraces all that the vessel is capable of carrying. Flanagan v. Demarest, 3 Rob. (N. Y.) 173. The term may be applied in such a sense as to include passengers, as well as freight, but in a technical sense it designates goods only.
-- Black's Law Dictionary
Legal Definition
The load of a ship.
-- Ballentine's Law Dictionary