Density \Den"si*ty\, n. [L. densitas; cf. F. densit['e].]

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.

Note: For gases the standard substance is hydrogen, at a temperature of 0[deg] Centigrade and a pressure of 760 millimeters. For liquids and solids the standard is water at a temperature of 4[deg] 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.

Source: Webster's Revised Unabridged Dictionary (1913)