What does density mean?
Density describes how tightly matter, people, or things are packed into a given space. In physics and chemistry, it has a precise meaning: the mass of a substance divided by its volume, typically expressed in grams per cubic centimetre or kilograms per cubic metre. A block of lead feels heavy for its size because its density far exceeds that of wood or water, and objects less dense than water will float. Beyond the laboratory, the word applies to any concentration within an area: urban planners speak of population density, doctors of bone density, meteorologists of fog density, and engineers of high-density data storage. Density can also describe figurative thickness, as in the density of a writer's prose or an argument. Precise yet versatile, the term carries a neutral, analytical tone and is indispensable wherever compactness or concentration matters.
The degree of compactness of a substance, especially the mass per unit volume of a material.
"Gold's high density explains why even small ingots feel remarkably heavy."
In physics this sense is countable when a specific value is cited ('a density of 19.3 g/cm³') and uncountable when discussed generally.
The quantity of people, animals, buildings, or other items present per unit of area or space.
"Manhattan has one of the highest residential densities in the United States."
The thickness, opacity, or crowdedness of something non-material or diffuse, such as fog, forest canopy, or text.
"The density of the fog forced the ferry to anchor until morning."
The plural 'densities' is used when referring to different measured values of density, often across materials, locations, or conditions.
"The report compared the population densities of Tokyo, Delhi, and Shanghai."
The densest naturally occurring element on Earth isn't gold or lead — it's osmium, twice as dense as lead and heavy enough that a litre of it would weigh over 22 kilograms.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of density
Density derives from the Latin adjective densus, meaning 'thick' or 'compact', combined with the noun-forming suffix -itas. It entered English in the early 17th century, likely by way of French densité, during a period when scientific vocabulary was being formalised. The same Latin root gives English the related words dense and condense, making them close etymological siblings rather than derivatives of density itself.
Related word forms
How density is actually used
Density is primarily a technical and scientific term but appears widely in everyday contexts such as urban planning, nutrition, and computing. It is an uncountable noun in general senses; when referring to specific measured values, phrases like 'a density of 2 grams per cubic centimetre' are standard.