The total amount per unit area of a material suspended in a fluid or in a cloud in space, measured along the length of a column.

(medicine) A measure of the amount of mineral in bones, used to estimate the risk of osteoporosis or fractures.

(ecology) Regulation of population growth by mechanisms controlled by the size of the population; especially the curtailment of growth by crowding, predators and competition

(probability theory) probability density function

(physics) The ratio of the density of a gas to the density of hydrogen at the same temperature and pressure.

The amount of light falling on a given area, as measured by units such as the lumen.

(sciences) A measure of the density of a material. The ratio of the density of a substance to the density of water at the same temperature. It is dimensionless and therefore has no units.

Average population per unit area; especially, the average number of people who live on each square kilometer (or square mile) of land.

(physics) The amount of electric charge per unit volume of space, unit area of a surface, or unit length of a curve.

(physics) A measure of the probability of finding an electron at a specific location within an orbital / (physics) A measure of the number of electrons per unit volume of space.