Milliliter. Definition: A milliliter (symbol: mL) is a unit of volume that is accepted for use in the international system of units (SI). One milliliter is equal to 1 cubic centimeter (cm 3), 1/1,000,000 cubic meters (m 3), or 1/1000 liters.. History/Origin: The base unit of the milliliter is the liter (US spelling), spelled "litre" in SI terms. The term "litre" was originally …