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

(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.

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

(sciences) The density of the particles that make up a powder or particulate solid, in contrast to bulk density, which measures the average density of a large volume of the powder in a specific medium (usually air).

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

(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.

(physics) A measure of rate of flow of a fluid, particles or energy per unit area

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.

mass per unit length

The mass of any given substance contained in unit volume.