A more thorough explanation:

Definition: Tonnage refers to the capacity of a ship to carry cargo or other loads, measured in tons. It can also refer to the total shipping tonnage of a country or port. Additionally, tonnage duty is a tax imposed on commercial vessels for entering, remaining in, or leaving a port, usually based on the ship's weight.

Examples: A cargo ship has a tonnage of 10,000 tons, which means it can carry up to 10,000 tons of cargo. The United States has a total shipping tonnage of 521 million tons. A port may charge a tonnage duty of $10 per ton for a ship weighing 5,000 tons, resulting in a total duty of $50,000.

Explanation: Tonnage is an important measurement for ships and ports, as it determines the amount of cargo a ship can carry and the amount of tax a port can charge. The examples illustrate how tonnage is used to measure a ship's capacity, a country's shipping industry, and the tax imposed on ships entering a port.