The weight (mass) of a substance in a given volume (of that same substance).
Examples of commonly used units are kg/m3 or g/cm3 for
solids, and kg/l or g/ml for liquids and gases. Referring to a substance's
density is to describe how heavy a substance is for its size.
Examples: water has a density of 1 kg/l, chlorine has a density of 3.1 kg/m3
and iron has a density 7.5 kg/m3. Link to weight units