The gallon is a unit of volume measurement used within various standardized systems, most notably the US customary and imperial systems. Historically and currently, it serves to quantify the capacity of liquids and other granular substances. There are distinct definitions for the liquid gallon depending on the geographic standard utilized, resulting in different volume measurements for the same name. Functionally, the unit is utilized in industrial applications, scientific measurement, and the trade of bulk commodities. Its use necessitates the clear specification of the underlying measurement system to ensure dimensional accuracy.