Matter exists in different forms known as phases of matter, primarily classified as solid, liquid, gas, and plasma. In a solid, particles are closely packed and vibrate in place, giving it a definite shape and volume. Liquids have particles that are close together but can move freely, allowing them to take the shape of their container while maintaining a fixed volume. Gases consist of particles that are far apart and move rapidly, filling the entire space available. Plasma, the fourth phase, occurs at high temperatures when gas particles become ionized, resulting in charged particles. Each phase has unique properties based on particle arrangement and energy.