Density is a quantity that is related to both mass and volume. It is usually denoted by the Greek letter "rho" and is calculated as

`rho = m/V` ,

where m is the mass and V is the volume. That is, density is mass per unit volume.

Mass is a quantity that determines how heavy an object is, and it is measured, in metric system, in kilograms. Volume determines how much room an object takes up, and it is measured in cubic meters. Density is the ratio of these two quantities, which determines how the mass is spread out over the volume. Density is measured in kilograms per cubic meter: `(kg)/m^3`

So, for two objects with the same volume, the object with greater mass will have higher density. If two objects have the same mass, the object with larger volume will have lower density.

By definition, mass is the amount of matter in a object and volume deals with the amount of space an object takes up. Density relates the two together in that it is the amount of matter (mass) in a given space(volume), which is why we calculate density using the equation

Density= Mass/volume.