A measure of the mass of matter contained by a unit volume.
The ratio of one quantity, representing something of interest, to another quantity representing space, area, or extent in which the thing of interest is distributed.
The probability that an outcome will fall into a given range, per unit of that range; the relative likelihood of possible values of a continuous random variable.
A measure of how hard a material is
The quality of being hard.
An instance of this quality; hardship.
The resistance to scratching, cutting, indentation or abrasion of a metal or other solid material.
The penetrating ability of electromagnetic radiation, such as x-rays; generally, the shorter the wavelength, the harder and more penetrating the radiation.
The measure of resistance to damage of a facility, equipment, installation, or telecommunications infrastructure when subjected to attack.
The quantity of calcium carbonate dissolved in water, usually expressed in parts per million (ppm).