A liter is a unit of volume measurement that is commonly used to express the amount of liquid in an object. It is defined as the quantity of fluid that measures exactly 100 cubic centimeters, or one-hundredth of a cubic meter (m³). The word "liter" comes from the Latin word for "liquid," and it has been used to measure volume since at least the early 18th century. In everyday usage, people often use the term "litre" as an alternative spelling of liter.