Den″si‐ty (dĕn″sĭ‐ty̆), n. [L. densitas; cf. F. densité.] 1. The quality of being dense, close, or thick; compactness; — opposed to rarity.
2. (Physics) The ratio of mass, or quantity of matter, to bulk or volume, esp. as compared with the mass and volume of a portion of some substance used as a standard.
☞ For gases the standard substance is hydrogen, at a temperature of 0° Centigrade and a pressure of 760 millimeters. For liquids and solids the standard is water at a temperature of 4° Centigrade. The density of solids and liquids is usually called specific gravity, and the same is true of gases when referred to air as a standard.
3. (Photog.) Depth of shade. Abney.