Hardness n. : The quality or state of being hard, literally or figuratively.

Hardness n. : The cohesion of the particles on the surface of a body, determined by its capacity to scratch another, or be itself scratched;-measured among minerals on a scale of which diamond and talc form the extremes.

Hardness n. : The peculiar quality exhibited by water which has mineral salts dissolved in it. Such water forms an insoluble compound with soap, and is hence unfit for washing purposes.

Example:
How would I test Hardness of gelatin for a science experiment?

Taxonomy
hardness, diamond, Indentation hardness, Scratch, rebound, deformation, resistance, scales, measures, exhibit, fracture, brittleness, hardness tests, plastic deformation, free encyclopedia, Materials science, hard material, pressure.

Defination from the web:
Hardness refers to various properties of matter in the solid phase that give it high resistance to various kinds of shape change when force is applied. ... In materials science, there are three principal operational definitions of hardness: ...