A "solid" is one of the three main states of matter, alongside liquids and gases. In a solid, the particles are closely packed together, which gives it a definite shape and volume. For example, a rock or a table maintains its form and does not flow like water or expand like air. Solids can be found in many forms, from everyday objects like ice cubes to complex structures like buildings. They can be hard, like metal, or soft, like rubber. The properties of solids make them essential for construction, manufacturing, and countless other applications in our daily lives.