Shipping units are a type of measurement used to quantify the amount of goods being transported. The two most common shipping units are TONS (4 letters) and SHORTTONS (9 letters). TONS are a unit of mass equal to 2, 000 pounds, while shorttons are a unit of mass equal to 2, 000 pounds, but with a metric equivalent of 1, 000 kilograms. Both units are commonly used in the shipping industry to measure the weight of goods being transported.