Cargo is the load of materials being transported by a vehicle like a ship, airplane, train, or truck, especially for commercial or professional purposes.
The word cargo is used it’s a singular noun that refers to a group of items. For example, all of the shipping containers being transported by a ship are its cargo.
Such a ship can be called a cargo ship or a A plane primarily carrying cargo can be called a cargo plane. Such a train is typically called a freight train is a close synonym of cargo). Cargo is often distinguished from other things that the vehicle might be carrying, such as passengers—the distinction is often made between a cargo ship or a cargo plane and a passenger ship or passenger plane.