Density

Mass per unit volume of a substance, commonly expressed in kilograms per cubic metre (kg·m⁻³) or grams per cubic centimetre (g·cm⁻³).

A cardinal invariant: the density d(X) is the smallest cardinality of a dense subset of the topological space X.

Mass per unit volume of a homogeneous material (ρ = m/V) measured at specified temperature and pressure conditions; a state property that links mass and volume and may vary with temperature, pressure and composition for fluids and porous solids.