Density is the amount of mass per given volume. It is expressed as density = mass/ volume

In ordinary terms, you can think of density as “how much stuff is in a given space.” Usually the space is considered a 1 cubic block, for comparisons. Common units for density include:  grams/ milliliter (g/mL) or  grams/cubic centimeter (g/cm3)

Density is an intensive property meaning that it is value specific to the substance, no matter amount. If you have a huge block of copper or just a small cube -- the density of both will always be the same, since it is copper. For this reason, if you have an unknown substance you can find its density and try to match it to a list of known substances and their density to help identify it.