: the quantity per unit volume, unit area, or unit length: as a: the mass of a substance per unit volume b: the distribution of a quantity (as mass, electricity, or energy) per unit usually of space c: the average number of individuals or units per space unit <a population density of 500 per square mile>
a: the degree of opacity of a translucent medium b:absorbance
Mass of a unit volume of a material substance. It is calculated by dividing an object's mass by its volume. In the International System of Units, and depending on the units of measurement used, density can be expressed in grams per cubic centimetre (g/cm3) or kilograms per cubic metre (kg/m3). The expression particle density refers to the number of particles per unit volume, not to the density of a single particle. See alsospecific gravity.