- The mass density or density of a material is defined as its mass per unit volume.
- An object's mass divided by its volume. Cotton has a low density; lead has a high density. Red giants have a low density; white dwarfs have a high density.  Gas giants have a low density; terrestrial planets have a high density.
Density in astronomyEdit
- The mean density of a celestial body is generally reckoned as its mass divided by its volume 
- The g/cm³ is a unit used to qualify a celestial body's density.
- As a reference, water density = 1 g/cm³.