Definition of densities:
(n) :
(physics) A measure of the mass of matter contained by a unit volume.
(n) :
The amount of a certain phenomenon (such as stuff, things, energy, or otherwise) in a given area (surface area) or volume (amount of space).
(n) :
The ratio of one quantity, representing something of interest, to another quantity representing space, area, or extent in which the thing of interest is distributed.
(n) :
(mathematics, statistics) The probability that an outcome will fall into a given range, per unit of that range; the relative likelihood of possible values of a continuous random variable.
(n) :
Stupidity.