Density and dense usually refer to a measure of how much of some entity is within a fixed amount of other space. Types of density include: In physics: Density, mass per volume Area density, mass over a (two-dimensional) area Linear density, mass over a (one-dimensional) line Planck density, Planck mass per Planck length Specific gravity, a dimensionless ratio based on the density of a substance to the density of water Relative density, a measure of density in comparison to the density of s… (More on Dense)