Answer: How much mass per unit of volume is in a substance
Step-by-step explanation:
Density is defined as the mass contained per unit volume.

It is fixed for a given compound at a fixed temperature.
Example: Mass of bromine = 586 grams
Volume of bromine = 188 ml
Putting in the values we get:
Thus density of bromine will be 3.12 g/ml and it is mass per unit of volume in a substance.