Thermodynamics: A eutectic is a property of a solid mixture in specific proportions that has a constant melting point (eutectic point) like that of pure substances.
The most well known eutectic is salt+water; salting the roads in winter lowers the melting point of the mixture obtained. The melting point of a eutectic mixture is lower than those of its two components.
Eutectic: pure lead melts at 325°C, pure tin melts at 235°C and the mixture of 38% lead with 62% tin melts at 183°C. This mixture is called the eutectic and the temperature of 183°C is the eutectic temperature.