Definitions of density on the Web:

• the amount per unit size
• concentration: the spatial property of being crowded together
  wordnetweb.princeton.edu/perl/webwn

• The density of a material is defined as its mass per unit volume. The symbol of density is ρ (the Greek letter rho).
  en.wikipedia.org/wiki/Density

• A measure of the amount of matter contained by a given volume; The ratio of one quantity to that of another quantity
  en.wiktionary.org/wiki/density

• dense - permitting little if any light to pass through because of denseness of matter; "dense smoke"; "heavy fog"; "impenetrable gloom"
• dense - having high relative density or specific gravity; "dense as lead"
• dense - slow to learn or understand; lacking intellectual acuity; "so dense he never understands anything I say to him"; "never met anyone quite so dim"; "although dull at classical learning, at mathematics he was uncommonly quick"- Thackeray; "dumb officials make some really dumb decisions"; "he was ...
  wordnetweb.princeton.edu/perl/webwn

• Dense - In topology and related areas of mathematics, a subset A of a topological space X is called dense (in X) if any point in X can be "well ...
  en.wikipedia.org/wiki/Dense_(topology)

• Dense is a 2004 35 minute made for TV film directed and written by Vanessa Williams (story) with Shari Poindexter which aired on Showtime and ...
  en.wikipedia.org/wiki/Dense_(film)

• dense - Having relatively high density; Compact; crowded together; Thick; difficult to penetrate; Opaque; allowing little light to pass through; Obscure ...
  en.wiktionary.org/wiki/dense

• The amount of matter contained within a given volume. Density is measured in grams per cubic centimeter (or kilograms per liter). The density of water is 1.0, iron is 7.9, and lead is 11.3.
  www.seasky.org/astronomy/astronomy_glossary.html

• The ratio of the mass of an object to its volume. d=m/V
  www.aerospaceguide.net/glossary/index.html

• A measure of the compactness of the matter within an object, computed by dividing the mass by the volume of the object. ...
  physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/GLOSSARY/GLOSS_D.HTM

• Density is the amount of development per acre on a parcel permitted under the zoning law. The density allowed could be four dwelling units per acre or 40,000 square feet of commercial building floor per acre, for example.
  www.squarefeetblog.com/resources/land-use-glossary/

• Density is the maximum number of dwelling units allowed by the zoning ordinance, based on lot size.
  www.scottsdaleaz.gov/BldgResources/DevelopmentTerms.asp