What is the meaning of Gallon?

A unit of volume, equivalent to eight pints

exactly 4.54609 liters; an imperial gallon

231 cubic inches or approximately 3.785 liters for liquids (a "U.S. liquid gallon")

one-eighth of a U.S. bushel or approximately 4.405 liters for dry goods (a "U.S. dry gallon").

A large quantity (of any liquid).

gallon

gallon (a unit of volume)

superessive singular of gall

superessive singular of gall

gallon

gallon (a unit of volume)

Source: wiktionary.org