Explanation: Specific gravity is the correct term for comparing the density (or effectively, the weight of a given volume) of a liquid to the density of the same volume of distilled water. It's a dimensionless ratio, indicating how much denser or less dense a substance is compared to water. This measurement is crucial in many scientific and engineering applications, including checking the state of charge of lead-acid batteries in amateur radio setups, where the specific gravity of the electrolyte changes with charge level. Specific mass is not a standard term for this comparison; "density" or "mass density" would be more accurate for mass per unit volume. Specific volume is the reciprocal of density, representing the volume per unit mass, and does not involve a direct comparison to water.