US fluid ounce (fl oz)
Definition: A US fluid ounce is one 128th of a US gallon, equal to about 29.5735 milliliters.
History/origin: The US fluid ounce came from older English systems and stayed tied to the US gallon after the US and imperial systems diverged.
Current use: US fluid ounces are used on drink cans, nutrition labels, recipes, and personal care products in the United States.
Cubic kilometer (km³)
Definition: The cubic kilometer is a huge metric volume unit. A 1 km by 1 km by 1 km cube contains 1,000,000,000 m³, or 1,000,000,000,000 L.
History/origin: Earth science needed a readable unit for massive natural volumes, so km³ became useful for water bodies, ice, rock, magma, and atmosphere-scale quantities.
Current use: Km³ appears in hydrology, climate reports, ocean volume estimates, glacier studies, volcanic eruption data, reservoir capacity, and large-scale geography.