From AMS Glossary
Physical law relating the change in vapor pressure of a liquid to the amount of solute dissolved in it.
The law states that P0 - P = P0xi, where xi is the mole fraction of the dissolved solute. The quantity P0 - P is sometimes referred to as the vapor tension of the solution. Consequences of Raoult's law are the so-called colligative properties of solutions, that is, the depression of freezing and melting points of solutions relative to those of the pure solvent and osmotic pressure. Raoult's law is observed in everyday situations every winter when we put salt on sidewalks to melt the ice. This is simply a depression of the melting point associated with the dissolution of salt in water.