The term for the amount of a substance that occupies a given volume is "density." Density is defined mathematically as mass per unit volume, typically expressed in units such as grams per cubic centimeter (g/cm³) or kilograms per liter (kg/L). Understanding density is crucial in various scientific fields, including physics, chemistry, and engineering, as it helps to analyze the properties of materials and predict how they behave in different conditions, such as buoyancy in fluids or the behavior of gases.