Define 'hardness' as it relates to materials.

Hardness in materials science refers to a material's resistance to deformation, particularly permanent deformation, scratching, cutting, or abrasion. This characteristic is crucial when selecting materials for various applications, as it indicates how well a material can withstand mechanical forces without changing shape or being damaged.

When we talk about hardness, we often consider how materials behave under stress and the implications of that behavior for their use in products and structures. For instance, harder materials tend to be used in applications where wear resistance is vital, such as cutting tools or protective surfaces.

Understanding hardness is essential for engineers and designers because it helps them choose the right materials based on the expected conditions and stresses during the material's use. This measure can be quantified through various testing methods, such as the Mohs scale, Rockwell hardness test, or Brinell hardness test, each providing insights into different aspects of hardness.