Solid refers to one of the fundamental states of matter characterized by structural rigidity and resistance to changes in shape or volume. In solids, particles are closely packed together, resulting in a definite shape and volume. Common examples include metals, wood, and ice, each exhibiting unique properties based on their molecular structure. The study of solids encompasses various fields, including Solid Mechanics, which focuses on the behavior of solid materials under external forces. Understanding solids is crucial in engineering and construction, as it helps in designing structures that can withstand loads and stresses effectively.