Σκληρό (Hardness) refers to the resistance of a material to deformation, scratching, or indentation. It is a key property in materials science, helping to determine how a material will perform under stress. Hardness can be measured using various scales, such as the Mohs scale, which ranks minerals based on their ability to scratch one another. Different materials exhibit varying levels of hardness. For example, diamond is one of the hardest known substances, while talc is one of the softest. Understanding hardness is crucial in industries like manufacturing and construction, where material selection impacts durability and performance.