Colligative properties are characteristics of solutions that depend on the number of solute particles present, rather than their identity. These properties include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. They are important in various scientific and practical applications, such as understanding how salt affects ice melting. When a solute is added to a solvent, it disrupts the solvent's ability to form a solid or vapor, leading to changes in these properties. For example, adding salt to water raises its boiling point and lowers its freezing point, which is why salt is used on icy roads in winter.