Eutectics

When a solution is cooled, it will freeze into a solid, or a solid will precipitate out of the solution. For many solutions, the freezing point will be lower for the solution than for the pure solvent. The mixture with the lowest freezing point is called a eutectic. (Pb/Sn phase diagram is based on a figure by Metallos, https://commons.wikimedia.org/wiki/Fi..., CC BY-SA 3.0.)