# What is density?

Density are:

• - 1. The state of compactness; the amount of matter per unit volume expressed in grams per cubic centimeter
• - 2. The measure of the degree of resistance to the speed of a transmission.

bone d. In clinical practice, the amount of mineral per square centimeter of bone;
usually measured by photon absorptiometry or by x-ray computed tomography. Actual bone density is expressed in grams per milliliter.
optical d. The light-absorbing quality of a translucent substance.
photon d. In radioisotope scanning, the number of counted events per square centimeter or per square inch of imaged area.
vapor d. The ratio of the weight of a vapor or gas to an equal volume of hydrogen.

The density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:
{\displaystyle \rho ={\frac {m}{V}}}…