Definition: A gallon is a unit of volume used in the imperial and U.S. customary systems of measurement. The U.S. liquid gallon (symbol: gal) is defined as 231 cubic inches, which is approximately 3.785 liters. The UK (imperial) gallon is larger, equal to approximately 4.546 liters.

History/origin: The term "gallon" originates from the Latin word "gallēta" or "galleta," a container or pail. Gallons were used historically in England to measure wine and ale, and different sizes were used for different liquids. The imperial gallon was standardized in 1824 in the UK, while the U.S. adopted its own version based on the Queen Anne wine gallon.

Current use: In the United States, the gallon is commonly used to measure gasoline, milk, and other liquids. The UK and some of its former territories continue to use the imperial gallon for certain applications. However, most countries around the world have adopted the liter as the standard unit for liquid volume measurement.

Definition: A liter (symbol: L) is a unit of volume in the metric system. One liter is equal to 1,000 cubic centimeters (cm³) or 1 cubic decimeter (dm³). It is commonly used to measure liquids and is equivalent to 0.001 cubic meters (m³).

History/origin: The liter originated in France in 1795 as part of the metric system and was originally defined as the volume of one kilogram of water at 4°C. This definition has changed slightly over time with refinements in measurement standards. The modern definition is based on the cubic decimeter.

Current use: The liter is widely used around the world, especially in countries that follow the metric system. It is the standard unit for measuring beverages, fuel, and household liquid products. In scientific contexts, milliliters (mL) and liters (L) are preferred units for accuracy and ease of use.