Solids are one of the three main states of matter, alongside liquids and gases. In solids, particles are closely packed together, which gives them a definite shape and volume. This means that a solid object, like a rock or a table, keeps its form and doesn't change unless a force is applied. Unlike liquids, which can flow and take the shape of their container, solids maintain their structure. For example, a cube of ice remains a cube until it melts. The strong forces between the particles in solids make them rigid and stable, allowing us to build many things we use every day.